actually you can train them all the way until they are 28 or so. They still will improve, it just becomes very slow.
If you focus pure on training, it's best to train them at their fastest, which is their first few years.
As I said, every time they age, it gets slower... so even though a 23 year old still improves, a 18 year old would improve much quicker, so if you keep training the 23 year old, you're loosing on training.
I personally buy players who are 22 or 23, and also still train them, but that's because the younger ones are either not yet good enough to play in my team, or way to expensive... But since I am in the top division in our country, I try to get as much succes as possible, and am placing training on the second row. In a while other teams will have been catching up, and will pass me, and at that time I will drop out, at which time I will have to step to an other strategy, and train youngsters in a lower division until I will be able again to compete at high level.
It simply is impossible to win the cup AND to become champ of a country at the same time if you want to train 18 and 19 year olds...
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. It's a choice you'll need to make at some time too I guess.
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