My parents always told me that school was more important than sport. I really regret listening to them

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Honestly, I gave up my sports dreams for school, and I so wish I hadn't. I'm an overqualified pharmacist with a PhD, who can't find a job that will work around kids. And the wages are terrible.
If I had my time again I'd do the sport while my body was young enough, and then focus on the academia later. Going to uni at 21 instead of 18 is no biggie, and I'd have done sports science or biomechanics, or something related to coaching, and had a career in sport, which is what I'm best at. Better money too!
So as I said I'd have few issues with missing school if we could work it. My issue is I have doubts over whether it is necessary before age 10. If you take all the 8/9 year olds starting out on elite track in the UK, a large percentage won't pass level 2 at 11 to enter espoir (HOPES to you, I think) and junior elite.
We have an 8 year old elite track kid who only trains 9 hours a week. She will pass level 4 easily on those hours, and probably progress without the hours. The club did try upping her hours to 15, but the kid just stopped wanting to go to gym at all.
DH and I often have this discussion about so many hours so young (he's a runner, so a sport where you don't need to build up the hours until later). I tend to agree with him- if you have an 8 year old putting in 25 hours a week to keep up with their peers, the hours are only going to increase and there will be a point where you can't do enough hours to keep on top.