I have 2 boys - 12 and 15.
12yo is moody, but no real signs of puberty, apart from general grumpiness. Still very childish and immature.
15yo started a year ago - sudden foot growth was the first sign - size 6 in July, size 8.5 by October, size 9 by December.
Became (for him) a little....rounded. Hes quite the athlete, so no spare flesh normally, but suddenly he had a bit of a paunch and, to his shame, slight moobs.
Then overnight he started growing very rapidly. 14cm in a year. Scrawny as a scrawny thing now. He was always quite stocky before, but no longer. BO. Hairy legs. Hairy pits.
He still has about 4 inches to grow, if he sticks to his red book targets. He is out of proportion - his torso is almost full sized and he is starting to get adult muscle definition - pecs and a six pack, but his legs are still out of proportion. Voice never really broke, just got progressively deeper.
I think 13/14 is about the age most boys start puberty, although some are much earlier and some much later.