The in game text says:
Turn back your level 10+ Dragons back into babies...but keep their level! For years our wizards have been trying to find a way to reverse the effects of aging, and finally they have done it! Unfortunately it only seems to work on dragons. Oh well. I'm sure that you'll be able to find some use for it.
Does this mean that I can turn a level 10 dragon into a baby so that I can start leveling it again? I'm not aware of another way to level a dragon past 10, but the tip itself refers to dragons "10+" so I'm thinking there is a way - and maybe this is it. It's a lot of coin for me at this point, so I want to be sure before I invest.