Anybody who’s so young to still be calling their penis a ‘peepee’ is probably too young to get hard erections yet. (And shouldn’t be on an adult site like Quora.)
And anybody who’s old enough that their penis gets hard probably has a good idea what’s causing it to become hard
It sounds more than just a little silly and childish for an adult male to be calling his penis a ‘peepee’.
I call ‘troll’ on this question.