Maturity
Bobby is seventeen.
This has been brought home to him in a number of boring, embarrassing, or useless conversations.
He's been told: 'It's a state.' Freezing a classmate is impolite and a little control would be helpful during emotional outbursts.
He's been reassured: 'It'll pass'. Everyone needs some time to adjust to being a mutant.
He's been lectured: 'Control is the essence of mastering your powers.' So please try and avoid bringing a glacier down on the school.
Bobby listens to what they say.
He's got his own opinion of course. Dealing with being a mutant isn't all that hard, it's the whole 'teenager' thing that's impossible.