You weren't immature, or did you mean the other guy in the thread?
Probably a typo. Anyway, yes, with inspiring creative people/artists we need to encourage them. Not mock them. Since this is the guy's first time doing it, I think he did a fairly good job. The paint aps were spot on and as he continues to hone his craft he'll get better.
But if you must absolutely critique someone's work, do it constructively. Again, mockery just makes people lose respect for you.