In the 36 seasons I've been playing I've only had 3 main strikers. All of them I've got when they were 18, freekick SA assigned straight away, and then trained up to 6*.
When they start playing well and scoring then I'd expect a man of the match award at lest one in 3 games, if not one in two. That way they with the extra bonus they sit at 6 or 7 * till mid 20's then slowly tail off till maybe 4 or possibly even 5 star in their early 30's.
My first striker had around 400 goals, my second 550, and my present guy is on 611 and he's still only 30.
Goalkeepers can keep up quite well as well, sign an 18 yo train him up SA stopper and 6* and he can play for years.
Most other outfiled players will struggle ot be viable for more than 6 seasons if you get promotion every season.
You can always not get promoted every 3 or 4 seasons if you want to keep more than a few of the team together.
And I never have a team of 6* players, usually around 3 *, that makes a difference, the higher your team average the more difficult it is to play catch up every season to keep it that way!![]()