The world record for under 18 is 10.19 and the medium for top sprinters at that age in finals around 10.4. Similarly, the fastest 16 year old result I can see is from the 2011 USATF National Championship by Khalfani Muhammad who ran a 10.55.
So, you're basically claiming your friend is amongst the top in the world of runners aged 2+ years older than him.
I call horse excrement on your claim.
Tennis players are lightning quick at what they need to do which is explode sideways for 2-5m the change directions and do it again, and again, and again. No track and field athlete could transfer over to tennis style movement and be as quick as any of the top players. The movement in tennis is too sport specific for linear runners to excel at just because they're super quick. Bolt for example never needs to slow down abruptly in any of his races but tennis players have to do it all day long.