Answering your question in the post tittle, players do retire eventually, usually start to think about it around 35, as for longevity Buffon (45), Pepe (40) and why not Kazu Miura (54), are obvious exceptions but also a rarity. Players retiring from FM is a realistic feature of the game IMO. As IRL you see a lot of players over 40 in non professional leagues, but in top flight is normal for players to retire before that age