Personally I think the opposite. Done properly, second XI cricket serves 3 purposes in my opinion. You have players who have designs on a first team slot, with the potential to do so. You have genuine 2nd teamers. And finally you have young lads coming up from Junior/3rd XI cricket, trying to progress, ultimately challenging for the 1st team or finding their place in the 2s. So for me a perfect 2nd XI would include players falling into all of those categories, even if it means some of the upcoming kids taking the places of some of the older, more experienced players where necessary. If done properly then the 3rd XI can be made up of a couple of experienced lads who maybe dont make the 2s any more, with quite a few younger players who are learning how to play the longer form of the game.
Granted this needs to be managed properly, and you need buy in from players - but in my experience when you are open and transparent with everyone, and have the numbers to back this up, it really does work. The last thing any club should aim for is a second team full of older players, and a third team completely full of kids. I actually think this approach sees the likes of South North/Benwell Hill etc fall down a bit. You play against their second teams and there isnt a promising youngster in sight. With a little more foresight they may bring a couple through into their first teams and save themselves a few quid at the same time.