Sorry, but no. Not only did I actually think he looked too old - I actually thought he looked older than he really was. He was like 26 or something when they filmed? He looked 35 to me. It's not that 26-year-olds can't play teenagers believably. But not every 26-year-old can do it. Some just naturally look older. And they things they did to make him look younger had the reverse effect. It's not his fault that he looked too old, but it's his and father's fault that they didn't have the self-awareness to realize it wouldn't work, and that they needed to cast someone younger.
Every single shot of Ben Platt in the movie made me cringe, worsened by the fact that his performance was one of the most appallingly terrible pieces of acting I've ever seen onscreen.
You're allowed to have a different opinion without trying to invalidate or undercut other people's opinions. I'm glad you enjoyed the movie! I wish I had. I enjoyed the show when it was Off-Broadway (never saw it on Broadway).