I would sell him if I found a marginally better player to train, at 18 or 19 years old.
hm. 18 or 19 years is not marginally better, it is WAY better to train.
If you meant you would trade him for a marginally less good player, but trainable because he is 18 or 19; then I think there would be a very big pricediffrence between both players, so he'd need reserve cash.
as for the question: my team is prety old, most of my players are also 25 or even older. I mostly opt to train more then just 1 position, and also more then 1 type of training, thus training my team slowly in it's entirety, with a level 4 trainer. And I do get some pops once in a while. Somethimes it takes 4 full trainings and between 7 and 10 secondary trainings (full training on an other type which has this skill as secondary) somethimes it takes more.
So I guess if you stick to 2 types of training, and each time on only 1 position, you should get at least 1 pop in each of the skills you train, but more likely you'll get 2, we are towards the end of the season now though, so he will soon be 26...
As long as they are 27 they still seem to train.
But once 28 I estimate skills will start to go down slowly, so if you never train certain skills, he will become less good on those. At that stage he will get training for all his skills to keep his skill-levels he has.
He will still go up in the skill you train him though.
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