I’ve been going to puerto aventuras a few times/year for many years to cave dive in the area. If you’re asking about the area in general, P.A. Is a big gated community with hotels, hundreds of condos, a big marina, golf course, lots of restaurants, things like that. It’s pretty self sufficient and it’s convenient if you’re there to dive. It’s not like ‘real’ Mexico by any stretch of the imagination, if that matters to you. One thing that’s pretty nice is that you can walk everywhere in there and it’s very safe and pleasant. There is a public beach, it’s not the greatest by local standards, but it’s right thee. Probably your resort has its own beach.
If you’re asking about the diving, I have never once gone diving in the ocean around there so I can’t comment. I’ve been to Cozumel more times than I can count and that is wonderful diving. For you staying in P.A., it would mean a taxi to playa del carmen (about 1/2hour) then the ferry to Coz. So doable but time consuming.
I have been in most of the cenotes that they offer tours in, and those are spectacular. Very different from true open water diving, but your son might not be ready for something like that with only 23 dives. You are in an overhead environment, and although there is visible light throughout, it’s very dim and you wouldn’t know it unless you covered up your light. They are proven to be safe in that every day hundreds of OW divers, some very inexperienced, dive in them and do fine. The few incidents I’ve heard of have resulted from OW divers straying out of the ‘cavern’ zone, which does have some light, and heading into the ‘cave’ zone, which does not and requires specialized training and gear. The reputable guides never take their clients into the cave zone. The cenotes do require good buoyancy and trim control and comfort with knowing that you cannot simply surface from where you are.
In terms of your gear, most people find that a 3 mil wetsuit is certainly sufficient for ocean diving (some people are fine in a rash guard only) and for the cenotes, 3 or 5 mil suit is typical. Those dives are not deep and they’re not long either, because you must reserve more air for the exit than on a typical open water dive.