The issue with this forum is that people want to take general statements (and I was clear that it was a general statement) and drag the debate into excruciating back-and-forth's about specific individuals. Happy to do that if you wish....Harry Kane was a famous 'late bloomer', an exception that proves the rule. Even then he was prolific from 21/22 and never looked back. Beckham made his United debut at 17 and his England debut at 21. He was a regular in the United side from 20. Roy Keane struggled to land a trial with an English club but eventually did so with Forest and almost immediately went from playing 'League of Ireland' football to starting in CM in the Premier League. Paul Scholes, despite his diminutive stature, made his United 1st team debut at 20 and scored two goals, becoming a mainstay from the following season (94/95).
Remember too, football was different in the early 90s. It wasn't the non-contact sport played on pristine pitches that it is today. There was a real chance young players could get seriously hurt playing against what basically amounted to hooligans in football kits (Vinnie Jones, John Fashanu, Duncan Ferguson, Neil Ruddock, Dennis Wise etc...) No wonder managers weren't mega-keen to chuck in 17 year-old children with that lot!
So despite you trying to name some players who disprove the notion (despite there really being no need to try to disprove a general notion), you've really just solidified the point. Which interestingly was defending Amad and re-iterating my belief that he should be given more time because he fits the profile of a late-bloomer.
We can go back and forth all day on the exact cut-off date by which a player should have shown 'elite qualities' and what the definition of 'elite' is....but I think most would agree that if, for example, Amad hits 23 and is still not a regular at United then he probably won't become 'elite'. That's why next season is a big one for Amad. This season proved he can be 'very good' after a somewhat worrying spell at Rangers. Next season, my point was all about the idea that he needs to step-up a level BUT still needs to be playing. So we should ONLY bring him back to United if we expect him to start 20+ games. Otherwise, he'd be better on loan at somewhere like Forest/Everton/Brentford etc....developing his skills in the PL
EDIT | one final comment, look at the very best Academy prospects we have produced post SAF. Rashford (in the team at 17), Greenwood (in the team at 17), Garnacho (in the team at 17). The rest (McTominay, Lingard, Henderson, Elanga, Garner etc....) might all become good/very good....but probably not "elite"