I think you have to draw the line at a certain age as what constitutes a young player. Players who are not young can have break out seasons too though. Amari Williams for example, he is 24 but has hardly played, clearly is not fully developed. Harper is 26, is he still "young"? Most players who are 25 or more are pretty much what they are. I had mentioned Walsh earlier, he is only 22. His issue is consistency. He played at a pretty high level at times last season.
Amari Williams is another one to watch in my view. He is back on a 2-way deal so the odds are against him for sure, but if he figures it out, he could really make a leap. He is starting out well behind the others as he really has not done anything yet. He has the most room to grow so in that respect, it favors him making a leap even though after a "leap" he still may not be close to a starter level player.
And Hugo, yes. I am very high on Hugo but as I said above, his big leap may not be this coming season. As to Mitchell and Cenac, I don't know enough about them at this point. I look forward to seeing them in summer league, although summer league does not always give you a good read. Walsh was horrible last summer and then stepped in and played some valuable minutes as a starter last season. My sense is Mitchell and Cenac may be more on the Walsh timeline.