You play each team in your division home and away so the league season is 18 weeks long.
When a player is going to retire it comes up on the players page.
As for "old" players, this might help from the training FAQ ...

3. How does players age influence the training?
The amount of training points players receive each training cycle steadily decreases after the age of 27 and after the players reach 31 they don't receive any training points at all. This is because they need all the training just to sustain their skills. After the age of 31 the players also start to lose points in their physical skills. See the list below for more info.
- Players aged 16 to 27 train normal and lose no points due to their age.
- Players that are 28 years old lose 25% of their training.
- Players that are 29 years old lose 50% of their training.
- Players that are 30 years old lose 75% of their training.
- Players that are 31 years old get no training points. They also lose from 10 to 15 points on Speed, Strength, Agility and Stamina each training cycle.
- Players that are 32 years old get no training points. They also lose from 16 to 20 points on Speed, Strength, Agility and Stamina each training cycle.
- Players that are 33 years old and above get no training points. They also lose from 21 to 25 points on Speed, Strength, Agility and Stamina each training cycle.
NOTE: No player skill can go below 12 because of his age.