It is one thing to have mature (Ryan Giggs) and experienced (Wayne Rooney) players in the squad, but as Chelsea are finding, you daren't retire too many at one time.
And although players who sign for United tend to stay for the longer term, there are still one or two gaps in terms of the more experienced players who will bridge them over the next five years.
So before you read this article, try writing down your own Under-25 team, in their correct positions and see why there is still a challenge to be addressed.
In compiling this team we have also included seven substitutes and used players who are currently on United's books, even though some may be on loan at the present.
For your further amusement we have included on the last slide an Under-21 team from those who remain after the Under-25s were put together.
But before we get into the teams, we have selected a captain (Phil Jones) and a vice-captain (David de Gea). The Under-21s captain would be Tom Thorpe; vice-captain Mats Daehli.
Manchester United vs. Villareal 2008
One of these players from five years ago still qualifies for an Under-25 team and yet we haven't picked him. Which one is it?
The average age of the team that we have picked is 21. Given that at least eight of them are already first team regulars, that is a big plus point for the future.
For comparison Manchester City have only six players under 25 in their first team squad and only Richards and Nastasic are regulars.
So here is our selection by position:
David de Gea has no contest and hopefully that will remain the same for the next 15 years in United's first team.
Rafael is, of course, chosen at right-back.
Given that they are twins and he was rated the better prospect when they joined United we have somewhat controversially selected Fabio as left-back.
Central defence is much easier. Unfortunately Jonny Evans is already 25 and so we have Chris Smalling and Phil Jones. The latter is also appointed captain.
There may also be some disagreement here. Our preferred tactical formation is 4-2-3-1.
So the two midfielders are Tom Cleverley and Nick Powell. The former will not let United down, and Powell must be given his chance as he is an excellent all-round footballer.
There can only be one choice as striker. Chicharito has the best strike rate for minutes played of anyone in the Premier League.
The three players behind him make use of individual versatility. In the modern game you have to be able to defend as well as attack.
In the comments on many previous articles, there has been the suggestion that Alexander Buttner could play in front of Patrice Evra in the future to get him game time. Buttner has played left midfield before and we include him here on the left side of attack. He has a powerful shot with both feet.
Danny Welbeck is a straightforward choice on the right side and, especially after his performance on Saturday, Shinji Kagawa must surely be played in his preferred position here, in "the hole."
At least two of the substitutes will have crossed the minds of some of you in assembling the team itself.
Anderson still hasn't rediscovered the consistent form he showed at the start of last season, so we gave Powell a chance instead.
Wilfried Zaha will surely become a United first-teamer some time next season, and as we haven't had the chance to see him perform in the Premier League, he makes the bench.
Ben Amos is the obvious choice as keeper as Anders Lindegaard is too old and Sam Johnstone is still only 19.
The big difficulty is who to back up as striker.
Will Keane is still not back playing after his injury last summer, and although he is surely an England star of the future we have preferred Federico Macheda. He was an instant hero at 17 when he scored the winner against Aston Villa, but he has regressed and might even struggle to get a contract this summer.
And if Angelo Henriquez is good enough to play for Wigan in the EPL, then he is OK to make at least the bench in this team.
We need another couple of defenders. Michael Keane and Scott Wootton have already featured for United's first team this season, so they make the selection here.
So who would be your team and substitutes? Make your selections now before looking at the next slide where we have chosen an Under-21 team to match the best.
Davide Petrucci now seems to be over the injury troubles that blighted a bright future when he was a youngster. He was Warren Joyce's choice as captain of United's Under-21s, but he is actually now 22.
Presently he is on loan at Peterborough, and his spell in the charge of Sir Alex Ferguson's son, Darren, could be make or break for him.
While Tom Cleverley had to go on loan four times before he finally made the breakthrough into the first team, we are not so optimistic about Davide. In any case, at 22 he is beyond our strict criteria and wasn't considered good enough for the Under-25s so he is excluded altogether.
The squad we have chosen, again in 4-2-3-1 formation is therefore as follows:
Marnick Vermijl Michele Fornasier Tom Thorpe (Captain) Sean McGinty
Ryan Tunnicliffe Adnan Januzaj
Jesse Lingard Jack Barmby Mats Daehli
Among the obvious talking points is the omission of Tyler Blackett, but we think Sean McGinty, with his height and all-round versatility, is the better prospect.
Tyler has gone backwards since the preseason tour, as has Larnell Cole and Jesse Lingard. But Jesse's recent goalscoring form might kick-start his season.
Finally we have chosen Jack Barmby ahead of Tom Lawrence because he is also a potentially better England prospect than his Dad, Nick, in our opinion.