Where to store luggage???

Can your landlord store the bags, until you check in?

Perhaps your flight will be late, passport control will be jammed with six A380s having just landed and the bus drivers will be on strike, and you get to your apartment at 1159.

I have not been to CDG, but what I have read on this forum makes my above comment not complete fantasy.

Hope all goes well and your landlord has some sort of storage, until your unit is ready.

If your landlord says that he cannot check you into your apartment until noon, he won't be able to store your luggage, because the apartment won't be ready.
If you don't want to go to the nearest train station, you will have to haul your belongings around with you.
I'd go to the nearest cafe and eat and drink something until noon.

"We had planned to take a taxi into the city, so won't be heading to a train station"

What's to prevent you from doing both? In other words, instead of taking a taxi to your apartment that won't be ready, take a taxi to a train station on the same Metro line as your apartment, after having made sure that train station has luggage storage. I say the same Metro line to make getting to your apartment easier once you pick up the luggage (or, of course, you can take another taxi from that station to the apartment)

Or, follow chexbres's suggestion, and hang out in a cafe near the apartment until it is ready. Remember that while you land at 7, depending on how long the lines at immigration are and if you have to wait for checked bags and how bad the traffic is on the way into Paris (all unpredictable), you may not have that much time to kill.

I had the same issue last year. I used City Lockers which has locations throughout Paris. I had the taxi from the airport drop me off at the unit closest to my apartment and explored the neighborhood sans luggage until check-in time.

There are luggage storage services like City Locker or Eelway or Blue Marble. As mentioned above, take a taxi to a train station or a luggage storage service and store luggage there or meet Eelway at CDG and have them take and deliver your luggage. If you have tons of luggage and go with the cafe option, please be mindful of the space constraints in cafes. You could be delayed but odds are that you will be in Paris by 10 AM.

We have left bags at apartments before check in time when staff was cleaning. It is not something to assume you can do and odds are good that they won't allow it or be able to manage it, but it is worth asking.

Otherwise, why take a taxi since the apartment won't be ready. Take the train to Gare du Nord and store the baggage and go get it and taxi to the apartment once you have checked in.

There are insurance reasons for why the owner/manager will not store luggage.

The rental contract specifies that the owner/manager will not be responsible for theft of personal belongings.

I wouldn't risk it, unless your luggage could be locked up securely, which isn't usually the case.
I also wouldn't go to all the trouble to go store your luggage someplace that's inconvenient - you didn't state where the apartment was located - but would just go to a cafe, instead.