3.5, not enough chest development to be mature yet based on that single pic at that angle.
Brisket hanging can throw you off, not the best marker for maturity.
When their is no distinction between neck stops and brisket begins is what i look for in pics, i would also say 3.5 based on chest vs hams and clear definition between neck and brisket in this particular pic angleHanging brisket when head is up is a pretty good marker, but with head down like that it's aking to your belly overlapping your belt when sitting. I agree 3.5 just from the one pic