My son already has a man's voice. But he's only 11! Normal?

[LaPalma]

My son started breaking his voice 3 months ago.
Now he has a very deep voice like a 16 year old guy ^^

The problem is, he's still very small (4.9 feet), he's still a head shorter than me. And he also has a rather childlike face.
When we go shopping together, strangers often look at us because his voice doesn't match to the age and height.

Do you think this is normal?
Usually the voice change doesn't come until the end of puberty, right?

Judging by DS' friends, I think it varies massively.

DS had a huge growth spurt in Y7 and his voice broke. One of his DF's voices didn't break until the month after they'd left Y11 and there's been everything in between.

Unusual but within the range of normal I think.
The voice of one of the boys in DD's class started breaking in y6 of primary.