I generally and anecdotally disagree on the peak age. If all things are clean and the racers are disciplined IMO that age is closer to mid-30's. That is taking the seriously gifted aerobic few, of course.The physiological peak age of a cyclist is probably closer to the age of these young guns than we previously thought. Add in the better talent discovery, elite training, and doping programs from a young age, and you get this. Cycling functions a lot more like 5-10k run races than marathons despite the long nature of the races, and those shorter events are always dominated by younger people on average. I do think 18-20 years olds as you specifically reference should not be quite top level yet, and some of those riders are surprising, but the age of people like Pog/Remco/Sheffield is not too surprising.
Having witnessed too many very talented world class level juniors quit before the peak their peak years almost to a rider was the same rationale: the sport requires you give up everything including your ethics on clean and healthy competition.
This CN article today pretty much indicates the same thing:
'We're not all like Pogačar or Remco' - Talented teenagers give up on dream of turning professional
By Stephen Farrandpublished 2 hours ago
Gabriel Berg and Cormac Nisbet quit while riding Soudal Quick-Step development team
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Soudal Quick-Step Devo team riders Gabriel Berg and Cormac Nisbet (Image credit: Soudal Quick-Step Devo Team)
Talented teenagers riders Gabriel Berg and Cormac Nisbet have given up on their dreams of racing professionally and left the Soudal Quick-Step development team, admitting the fears and pressures of the sport had left them unhappy and looking for a different life.
Fortunately both had the courage to stop racing before suffering any major problems. They were both grateful to the Soudal Quick-Step development team for supporting them during their racing career and after they made the decision to leave the team.