What is max age till which a boy's height increases?

Most stop at 17: Growing bones have plates of new growth located just before the bone ends. These growth plates have less density than bone & show up on xray as a dark line like a crack. As long is there are actine growth plates, there is potential for more growth in that bone. A hand xray is often studied in short kids to see if they have more time to grow. A few grow into their 20's.