So I took Netherlands in a new league of which moderator is osm and one weird thing I noticed that all my players are 26 yo , not that only but every single player from every single team in the league is 26 yo .
Weird bug (I think)
You're right, the ages in real life differ a lot. But that is a choice from the creator of the league. Don't know why they did it, but it's not a bug. Just a weird choice from the league developers.
The reason all the players are 26 years old is because you're playing in a special league where transfers are not allowed. This way there is a chance you can improve players on training that would be very old and not easy to train if they used their normal ages.