First time Backpacking through Europe

This is not too aggressive for 22 year olds who are full of energy and there to party.
if this what they want to do and you or they can afford to do it go for it.

They should try reviewing hostels before they go (they can meet babes in hostels from all over the world and at least there is some vetting you have to show a passport stay there)
http://www.hostels.com/

I would book the first place in advanced four sure and Amsterdam well in advance only because I showed up there and there were no beds and we just had to stay awake all night horrible. On 2nd thought It can not hurt to book everything in advance that way they have to stick to the order. Not to mention it is much cheaper than just showing up. You can lose time energy showing up and running around finding place to stay.

You don't say if they have the plane ticket already. If you specify that we here on the forum could perhaps pinpoint a better order to visit each city listed..

Also buy insurance that covers medical and evacuation costs for the duration of the trip if you have not.

My thought is that there surely must be some places closer to home where they can party with babes, and save a lot of money on travel costs. It seems like a waste of a visit to all these cities of great historical and cultural significance, if that's all they want to do.

But if they're set on taking this trip, make sure they're educated about the possibility that some of those "local babes" may be scam artists.

But if they're set on taking this trip, make sure they're educated about the possibility that some of those "local babes" may be scam artists. Unless these young men are particularly good-looking, well-dressed and well-behaved, I would suspect that if they are approached by one of those "local babes", it almost certainly is a scam or an advertisement for some kind of "date bar"... which despite the name, would be one of the last places on earth you would take a real date.

I recommend they also do some reading on human trafficking in Europe, lest they inadvertently find themselves patronizing such an institution.

they need to take a close look at the transportation costs between all these locations. The time spent in transit will dampen any partying plans.

Which hostel are they staying at in Berlin? If it's too much of a schedule, drop Barcelona.

As K Reeves in his 1980s' film said, "party on dude."

Stan said

they need to take a close look at the transportation costs between all these locations.

That was my first reaction: Party until late then try to rally for a train every few days. Then again, most places force check-out by 10:00AM, so they'll have to move along on check-out day. There are some very long segments in this itinerary. Perhaps they should research the trains before leaving the U.S. so they have an idea of how long the transfer days will be.

EDIT: I like to use Rome2Rio to estimate transit times.

BTW Barcelona to Monaco is about 8.5 hours by train. Maybe drop Barcelona as an outlier.

Hmm ...hope they have all gotten "the talk" about STD's, safe sex, and big-city-ladies. (Also hope they have figured out how to finance this trip without depending on an emergency call to Bank of Mom and Dad.)

Sounds like Eurotrip. Teen sexromp movie that is a total stitch, full of pre-conceved notions and fantasies.
https://en.wikipedia.org/wiki/EuroTrip

As advice in your previous post, fly Barcelona to Rome, skipping Monaco. Night train Venice to Prague (via Linz)? Brussels is not a party capital, try Ghent.

It will be an eye-opener.

"Hmm ...hope they have all gotten "the talk" about STD's, safe sex,.."

Come on now these 22 years old are grown men; you would not baby them when they go off to the military would you?
We had an outbreak of foot and mouth disease on our college campus.

As a 22 year old, they will have enough energy for a trip like this. When I was 20, I spent two months backpacking Europe on a fast pace. My trip was not drinking my way around Europe, but it was fun. They will have fun. The good hostels have a reputation and will fill up fast. You may want to mention this. A good hostel or bad hostel can change the experience they are looking for. For you, if they booking early, it helps you keep track of them.

They should look at Andy Steves’ Europe: City-Hopping on a Budget: https://store.ricksteves.com/shop/p/andy-steves-europe-city-hopping-on-a-budget. Andy is Rick's son, a recent college graduate himself, and his book is directly geared to their interests - stays of a few days in a city, with a bit of sightseeing and a lot of meeting people and partying.

Yes, getting between all the cities you listed will eat up a lot of time and money; I'd cut a few just for those reasons, not because they aren't great places. Well, I'd definitely cut Brussels because I think it has little to offer (unless they're into one of the museums there), and I think they'll find Monaco very small, very expensive, and not really geared to their interests (unless they're into aquariums and gardens, in which case they'll like it fine as I did).

Lots of stereotyping and assuming the worst in some of the comments above. I think it's only normal that young people choose to mix travel with having a good time. If they have come up with this itinerary, then to me it indicates they are pretty serious about the 'travel' bit.
I'll offer my encouragement and a few observations.
1. Monaco is expensive and Barcelona-Rome is a long way by train. Fly this leg (and add a night each to Florence and Venice).
2. Consider the night train from Venice to Prague (via Linz or Vienna).
3. Research hostels thoroughly and book ahead. Obviously this means locking in the itinerary, but I think rigid structure is something young men appreciate (and sometimes need).
4. Trains will pretty much all need to be reserved in advance, even if choosing to purchase Eurail passes. Here again, do your research.

If their goal is is nightlife and opportunity to mingle with others their own age, I think they have chosen some great cities. I agree with David about some of the previous comments. You can mingle with locals and meet people and be smart and responsible at the same time. They are probably more likely to meet other tourists their own age rather than locals but you never know!

I try to avoid itinerary posts because there are so many differing opinions, I hate adding to the mix. But a few things jumped out at me.

1. How are they getting from Barcelona to Monaco and on to Rome? Those are loooong train rides. Monaco is also fairly expensive and I'm assuming they have more of a backpacker budget. Maybe cut out Monaco and get a cheap flight from Barcelona to Rome.

2. How much do they really want to see Venice? If they really have an interest, keep it on the itinerary. But if it's on the list and "just because" and they are looking to add time to other cities, I would consider skipping it. It is fairly expensive to stay in the city center, inconvenient to stay outside of it if you are only staying for one night, and has the least amount of night life.

3. What were their plans for Florence? Florence is a lot about art. If they have an interest in touring the museums, I would add an extra day to Florence. If they have absolutely no interest in those things what about skipping florence all together and going to the Cinque Terre for some hiking and beaches? The Cinque Terre are not a good day trip from Florence which is how a lot of people try to do them.

Would love to hear how the trip went when they get back!

EDIT: It's helpful to think of number of nights in a city, rather than days, when making an itinerary. Assume that the travel day between cities is a "lost" day as far as sightseeing.

Very helpful advice, bought the book, doing more homework.

Partying around Europe without going to Ibiza???? Ibiza is probably the #1 EDM and party spot in Europe...maybe the world.
I think Ibiza would suit their plans more so than Monaco.