It's 5 handed, and didn't you see this: Button raises to $1, 1 fold, HERO raises to $5.25, UTG folds, Button raises to $16.

With no reads, that's either KK or AA, and only a slight possibility of QQ. He could be BSing around, but don't risk your stack on that with no reads.

I play 6-handed and KK vs AA comes up more than you think.