I've stayed in both..YC and the regular part of the ship. Even when in YC, the Wife and I get out a good bit into the regular areas of the ship. I think MSC has a good product...
You'll be just fine on Celebrity. My Wife and I are in our 50's...been sailing Celebrity for a while...we have met many great younger and older folks on board. These boards can be a bit misleading..I never hear the griping/sniping I see here on board.