Actually, it very rarely begins on the track. There's been a few recent pick ups from school sports development programmes straight to track cycling, but most careers start in time trials, cyclocross and mountain biking. There's some influx from grass track cycling but it's a waning sport, much to our loss. All the regional cyclocross and MTB leagues will have racing available from age 8 upwards, sometimes younger. It's a good way to assess a child's aptitude for the sport and competitive riding. It also delivers a pretty rigorous training in bike handling which is always valuable. If you're looking for sprinters and fighters, it starts here. TTs start at 12 (CTT regulations) which have always been good for showing who has that built in power capability. From there, if there's local access, it's junior road race leagues.
The track just coalesces any skills and talents and then builds on them. By the time the riders get there, it's usually pretty clear who the sprinters and pursuiters are. It's a very good development arena though. You're in a closed environment every day under very close scrutiny of your sports managers with an almost competitive amount of discipline.
It's interesting though, there's some pro riders out there to who track is a no go area. They've got all the qualities of strength, power, focus, discipline, handling but something about the boards doesn't work for them. I've even seen really competent riders who ride fixed wheel bikes who ride all over the place and happily blast around city traffic with no real worries. But as soon as they hit the boards, the brain just has a really big nope moment and refuses to play.
Speed skating would be a lot more exciting if they bought in keirans, madisons and omniums.