Eye-balling this, the 90th percentile 16 year old is about as tall as the 80th percentile 20 year old, and as heavy as the 75th percentile 20 year old.
Conversely, the 50th percentile 20 year old corresponds to like the ~55th percentile 16 year old in height and like the 75th percentile 16 year old in weight.
While true, this isn't the right way to analyze this. The right question is how much strength or size is necessary to operate a modern powerful chainsaw with a sharp chain. The answer is "not much". You need to be able to position a ~15 lb (7 kg) saw at waist height for a few seconds until each of three cuts is started. With a sharp saw, the forces are negligible after that for 2 of the 3 cuts required. With good technique, you can even use leverage against the trunk for the one short upward cut. There is considerable skill involved, but brute strength is not a requirement. While you are presuming a male 16-year-old here, I wouldn't be surprised if most female 14-year-olds were physically strong enough.
Eye-balling this, the 90th percentile 16 year old is about as tall as the 80th percentile 20 year old, and as heavy as the 75th percentile 20 year old.
Conversely, the 50th percentile 20 year old corresponds to like the ~55th percentile 16 year old in height and like the 75th percentile 16 year old in weight.