Nosebleedboy (NBB for short) is very firmly in the late developer camp...
Didn't start playing at all until the age of 8.
Didn't have a lesson on his own until 10.
Didn't join any kind of musical group until going on 11.
Didn't take any exams until the first few years of secondary, and has only taken 6 in all, across 2 instruments - one G4, 1 G5, 2x G6 (needed for senior county ensembles, which he wandered into along the way) and 2x G8 (because he decided after GCSEs that he'd like to go on and do music, and he and his teacher decided that if he was going to do so, then getting G8s would be handy).
Did the 2 G8s aged 17, in two adjacent terms of Y12. Did a late audition for JD in his specialism (not classical) in the summer before Y13, and auditioned for full-time conservatoire courses in the autumn of Y13.
Got into his first choice, with a choice of which of the 2 instruments he would like to study.
It's not always comfortable, doing things 'by the whirlwind' rather than 'by the normal route'. But it's certainly possible....