I would like to start off by saying how much I have enjoyed FMH, from 13 to 15. However, this version has a few bugs, and one is the stamina bug. Anyway, here's my basic attempt at analysing how stamina goes down over the years.
I just did a very quick player search from a small database with Scotland loaded to find out just a little about its effects.
This means that of 3707 players, 81.20% have stamina of 10 or higher and 22.09% have stamina of 15 or higher.
This means that of 3596 players, 72.27% have stamina of 10 or higher and 19.27% have stamina of 15 or higher.
In just 5 years, the amount of players with what you would consider a decent stamina has dropped by over 10%, while the number of players with a green attribute for stamina has dropped by more than 12%!
10% may not seem like much, but just think, in a squad of 25 this could affect up to three of your players. I'm sure someone else could do a more detailed study, but that's my bit.