Players can announce their retirement once they turn 32 (33 for goalkeepers). The older he is the higher the chance is that he will decide to retire.
When a player announces to retire it will always happen during the season update and the player will always play the full season ahead before retiring.
Once a player has announced his retirement he cannot be sold.
Factors affecting retirement age
Retirement is random.
Player skills, club facilities don’t influence on retirement.
Does anyone know how decide players’ retirement?
Only age and luck decide their retirement?
Other factors like Skills (Strength, Stamina, Workrate), Hidden skills (Professionalism, Injury proneness), Player level (Recommendation, Skill Index, Routine) , Facilities (Training Grounds, Physio, Medical Center), etc affect retirement?
Retirement is all down to random, or if you prefer, luck.
Although there is no reliable proof, players on the transfer list during the season update might have less possibility to announce the retirement.