Our teens were 13 and 14 when we did two cruises on the Liberty and they loved all the amenities on that boat. They did rock climbing, water slides, ice skating, pools, plus shows, etc. They were never bored on that ship and it wasn't particularly new at the time we were on it (2018 and 2019).
I think older ships have tons for kids to do on them. We've always sailed by price, so we haven't even been on the newest and biggest yet (about to go on Ovation in September and looking forward to that).