If his FEET are still growing... then he definitely is no where close to done.
In theory, feet start first and stop first.
At 14, difficult child's feet have "stabilized"... the rest of him? well... his over-height extended family see him on a regular basis, and THEY say "hey, dude, SLOW DOWN or you'll be going through the roof".
Short-sleeve or sleeveless shirts, and shorts, are fairly safe - "loose" is in, and height shows up most on arms and legs. Pants? jackets? well... I buy ahead... by about 3 months.