The quick answer is that you sell the old players on your team when they are no longer good enough.
But how do you define "good enough"? And what other factors should you consider?
At what age to sell your old players?
The reddit user zizou00 said:
Every club's situation varies, as does their wage budget and youth talent.
The only general rules I use for replacing older players are "does the amount they're going to play justify their current wage?" and "is there a younger player who can do the same job that needs minutes?"
Older players can be vital to your short-term performance, and there's an element of known quantity about them. You know what you're going to get out of them.
Just like the old adage "if they're good enough, they're old enough", "if they're good enough, they're young enough" also applies. Some players will still perform at 37 as they transform and their skillset evolves.
The reddit user theslothening argued:
I only sell them if they are no longer performing well.
It can be extremely valuable to have players in their 30s who are excellent team leaders and mentors for the younger players.
These older players likely already have partnerships with other players and it can take a long time for new players to establish those same good relationships.
I find little value in bringing in new players just for the sake of it if the older players are playing well. Consistency wins in FM (and IRL).
The reddit user TheDaftGang added:
In the past I made the mistake to sell a great player who was 31-32, to let the young 19 y/o have more play time.
Turns out the 19 y/o never reached what was expected of him and had to replace him after a 4-5 years and sell him.
While the 32 years old was still one of the greatest players in his position until he was 36 or something and kept playing until he was like 38 or 39, and still being at a very good level.
I could have kept him a few more years and would have done way better.
As you can tell by now, there are several factors you need to consider before putting one of your old players on sale.
Should you have old players in your team?
Jake answered this on a video done during FM21, but it contains some universal advice. Check it out.
To wrap it up, here's an opinion I personally agree with:
Sell them before they turn 30 to get the best possible transfer fee, UNLESS they are long serving players.
If that's the case, you should NEVER sell them if you can afford their wage demands.
There's some sentimental value to this opinion, don't you think? 😊