They are 15 at the time. At this rate, Tadano-kun will only be able to confess at... 18? 19?
Anyways, I like how he proposed her to go danse. And I guess it's the only reason "author's will" decided that he will crossdess all the festival - so that he will be disguised when coming to danse with Komi-san. To evade whole school's... vengeance