Four full days in Paris oui ou non for Versailles?

I agree with the others in playing it by ear. My trip to Versailles helped put my perceptions regarding the bloodiness of the revolution into better perspective. It is absolutely incredible to wander around even just the small amount of the palace that is open to the public.

You might be surprised at his reaction. My teenagers thought they would die first rather than see it and the Louvre and once got there, they did not want to leave. What does he say about it?

I think you should play it by ear. Paris is great for that. What doesn't sound interesting to him in theory could blow him away when he sees it. After London and Italy, you both will have a better understanding of what you both like. It also depends on the weather. I wouldn't go on a rainy day, for example.

I think he'd like Versailles. It's only about a 20 min. train ride. He might also enjoy the military history museum.

I tend to agree with the playing it by ear advice. Versailles is close enough that you can decide at the last minute that you want to check it out. For a 22 year old son who has evinced much interest in Pompeii (ruins! casts of dead bodies!) and isn't so much into art or history, Versailles might be a bit of a slog. It is, after all, a big old mansion, stuffed with fancy furniture and art and history. :D And yes, of course, he might love it if you do visit. Just seems that if he doesn't, you've sunk at least half a day. If you haven't already, why not have him check out their website? Its pretty fab, and would give him an idea of what's there, and whether or not he'd like to check it out. http://www.chateauversailles.fr/homepage

I think a lot of people skip Versailles because they think of it as yet one more giant palace with stuffy old furniture and paintings of royalty. He might not enjoy that. But... There is NO need to tour the palace. One can fully appreciate the chateau by strolling and exploring the gardens. You'll sense the enormity of the palace itself just from the outside. Consider a tour of one of the Trianon's on the grounds to get a sampling of the interior. Have a picnic along the grand canal. Rent a paddle boat on the canal. Rent bikes to ride around. There are so many options. Play it by ear as someone suggested. It's an easy ride out there and not taking a palace tour allows you lots of flexibility.

When my husband and I were 22, he was in an University of Illinois year abroad architecture program. His classes were in the former stables of the Palace across from the entrance. We visited the gardens of the Palace many many times, and did not visit the interior until the last day we were in France. It is the gardens you want to see: the canal, Marie Antoinette's hamlet, the gorgeous landscaping, fountains, flowers, more and more. As PP mentioned, you don't need to go inside at all. But play it by ear!
Bobbie

I agree with everyone else. And, as Douglas mentioned, you can rent bikes and ride all over. That's our favorite thing to do there. My son is 21, has been to Versailles many times and loves it (inside and outside).

I recommend looking into the Fat Tire Bike Tour( http://www.fattirebiketours.com/paris) of Versailles. They usually have some room for walk ups or late reservations. My wife and I just took their Versailles tour, Aug 14th and really enjoyed it. I documented it in the following blog entry: http://engineeringatravelplan.blogspot.com/2011/08/vacation-day-11-another-bike-tour_14.html
One word of warning, Versailles was packed. If you don't like crowds, I suggest strolling the grounds around the Grand and Petite canals. The entrance line to the Chataue looked intimidating, but it only took 35 minutes to get through.