..On the cusp of puberty
for some, late for others. There is a 13-year old in my pediatric practice only 4'7"; another, almost 6 feet! go to cdc website @ www.Cdc.Gov; type "growth charts" in the search box at the right upper corner of this webpage; click thru the menus until see boys charts geared for age13. Plot your son. He's probably ok.