That would be amazing, but I think that would be really OP for a low-level party. the lowest rating for young dragons is CR6; and those cannot even polymorph, unless the rules changed.
https://www.dndbeyond.com/monsters?filter-search=&filter-type=6

I remember that half-dragons in pathfinder were banned by some GM because they are too overpowered, and you have the size problem in some settings. And they are only half-dragons, xD

Maybe they can delay the recruitment or something like that.