I swam my first 25m at 16
I learned to ride a bike at 19
(I learned to run at 32... maybe I'll do a triathlon one day)
DS is dyspraxic... I suspect there is a genetic link going on.
He can do both, but he's had swimming lessons since 4 (plus baby/ toddler lessons before that) and I've kept him going into his teens and is now Stage 8. Sibling rivalry helped with the bike riding- DS2 got the hang of it at 4 and motivated DS1 to not be beaten and they both cracked on the same day. After going through teen years not being able to swim/ ride, I didn't want my children missing out.
I decided to go to adult lessons at 16 for my DoE sport which took a bit of courage and was very much an outlier amongst the pensioners there. There was an instructor in the water who could actually show me how to swim rather than yelling into the echo and flailing limbs like the 5 years of school lessons that achieved nothing.
It took 4 months of 1:1 lessons to get my 25m badge, and 11m after that I could swim a mile.
Bouyed by the swimming, at 19, I spent my first week of salary at my student job, bought a bike, walked it home and spent the weekend throwing myself off it until I cracked it. It was easier on an adult bike than children's bikes had been with their small wheels.
I remain a strong swimmer and can swim a mile in open water. Cycling I can do for basic function and fun.
DM didn't like either activity so never put any extra into facilitating learning either skill. Cycling wasn't instinctive to me and playing on other people's bikes wasn't enough to crack it.
I'm so glad I learned!