Could total sexual abstinence stunt teenage growth?

No stunting. No. Believe it or not there are plenty of teens out there who are sexually abstinent and growing quite well.
It sounds like. It sounds like you are worried about a child of yours. Kids develop sexually at different rates, just like they start walking & talking at different ages. If you are concerned about their social development, you can always speak with a psychologist, but your teen's physical growth will be fine.