When does puberty start for guys?

im on my older sises account n im 12 n i havent had the talk about puberty n that crap n i think i started it i have hair round my guy part and under my arms but my dad doesnt have any chest hair so he dsnt think i will. n i think my lil bro is startin puberty? hes 9 n he's changin like a lot n is that to young for puberty? i know ive started n i dnt really need the puberty talk but i think he does n i told his dad (my step dad) i'd give it to him cuz hes not here a lot but i gotta know what happens and if 9s to young. thx.