For Zlatan maybe this will be the end for him as previously promised because regardless of his current age it is enough to retire there even he can retire with pride because he can win the title in his last season
Winning the title at the end of the season and scoring 8 goals and 3 assists in 23 appearances in Serie A seems very special to a 40 year old man like ibrahimovic. It was a huge achievement for him and now I think he is very proud to announce his retirement
"if he will do it this time". It will be difficult for Milan to achieve the same feat next season
"although it is possible" if Ibrahimovic decides to continue his career, so retiring is the right choice for him in my opinion.