why U21's and Not Reserves

[scs1mon]

why is it labelled U21's when you can drop any age of player into the so called u21's ????

[Damedius]

Check the rules for the league they play in. Usually you are only allowed so many players over 21 to play in each match.

[Vali]

It depends on the country and the league. Some countries have also a reserve team, and youth until 18 etc..

[zeeb]

You can put them in the team, but that doesn't mean they're eligable to play.
Same with any team and sub-team really. If they're not allowed to play according to the rules, they can't play.

So you can put your entire team into the U21, but anyone above the age of 21 will not be eligable to play by default, then there might be foreign rules or non-eu rules on top of that as well, but that's another topic.

[JigglyEmz]

that's probably because most nations now have priority over u21 teams rather than old fashioned reserve teams... a limited amount of o21 players can play same way a limited amount of o18s can play in o18 matches both dependant on each nations rules. its realistically used for fitness of players returning from injury or not quite at first team level, i think irl reserve teams and their leagues were essentially scrapped because too many of the top 6 or so clubs were basically stockpiling the best players o21 that werent quite ready for 1st team. so they were scrapped in favour of giving youth more of a chance and aidding clubs outsid the top 6 or so struggling to sign quality players because they were all going to those bigger teams reserve teams... but ai teams abuse it in game have done for a few years now sadly SI have done nothing to stop teams abusing it.
theyve done it quite wrong here for some teams, like changed some teams from B Team to U21 team that IRL have a B Team but not a U21 team take Brentford as an example they have a first team, b team, u19s team, u18s team and the 2 womens teams (obviously not in FM24). but in game Brentford have a first team, u21s and u18s. don't know if thats a database flaw or if its intentionally. not many nations use reserve teams now some havent for a while there was a short experiment like 1 or 2 seasons with teams going from u21s to u23s but they are now back to u21s and your still seeing the effects of that on some teams, who gave some of their 20-22 year olds new contracts to cover prolonged development team only for the experiment to be scrapped, in england some do way down the pyramid like Sheffield FC Reserves play 1 or 2 tiers below the first team and im pretty sure IRL Brentford B actually compete in a lower pyramid league and cup
would love to see them add some sort of system where ever year managers vote on rule changes, additional leagues etc or even just random changes like they did with brexit way back when now... that could say implement a b team league, reserve league, change u21s to u23s or other way, change u18s to u19s or other way etc. wouldnt it be funny to see say English leagues implement B & C Team Leagues or even allow B/C II/III teams to form and compete lower down (which is where they should atleast add the ability to see whats going on in those but as non playable)
personally i think we should still have a reserves/b/ii leagues with a limit like currently on u21s in england so say only 5 o21s can be used. or like in some nations allow them to play in lower leagues (would need to be expanded which is where reserve leagues would be more beneficial) with a restriction to how high the teams can be promoted so say cannot be promoted into national league/north south would do for me. add an EFL League 3 back in and maybe some more tiers further down