Adolescents 12 yrs-13 yrs
Adolescents are dimensioned with 50 percentile measurement data which is also the mean or average value. All data was compiled from people without physical disabilities.
Human dimensions vary widely among the "normal" populations. They will vary more widely for people with developmental and physical disabilities.
Keep in mind that these dimensions are presented for size estimates, not precise fitting. The dimensions are intended to assist you in making a better choice of equipment size. If you know the person's total height, the other dimensions listed should be of help to you.
Also keep in mind there are big measurement differences in sex, ethnic, and racial context. For example, seat heights vary. Consider the mean of 17.5" for the average white male sitting height, for black males it is 18", and 15.8" for Japanese.