I wouldn't be surprised if there won't be any growth stages like juveniles or something. With 75, and likely more to come, dinos, that's an insanely huge amount of models, rigs, meshes, etc. in comparison, especially more work must've been done on not only the dinos (including the non dinos), but on everything else as well. Budgets and time are a huge thing in the industry, you know. And the only reason why indies were able to do this is because they aren't as "restricted" with what they have as AAA teams like Frontier are, despite given just a few extra more months for this game. And Planet Zoo accomplished breeding and growth stages because things were different in comparison.
But, if there will be "young" dinos in any way, shape or form in this game, then it probably just might not be the kind where they roam around with the adults or even spawn from them. Or at least, that's what I can guess until more of the game is known or until after launch.