Harry Potter and the Aging of the Phoenix

I’ve just heard TWO people (one Larry King) ask Daniel Radcliffe if he thinks he’s “too old” to keep playing Harry Potter.

Um, is no one aware that the character is aging? Do they expect that he’s still playing an eleven year old? Radcliffe is currently 17 and he’s playing a 15 year old (Fifth movie). What’s the problem here? Alyson Hannigan was 24 playing a 17 year old on Buffy the Vampire Slayer. No one gave her grief about that.