Giroud still has the chance to play in Serie-A, but the physical factor that is easily affected by injury makes Giroud have to be careful when playing. if there is an accident on the field, as was the case with Ibra, Giroud will take longer to recover since the age factor and the frequency with injured history so far. However, if he manages to protect himself from potential tackles or body charges that injure him, I think Milan have the chance to play Giroud longer.
Giroud's performance during the World Cup was quite impressive. He scored 4 goals to help France be in the final. But unfortunately, he only got 40 minutes of time in the final because France failed to develop their game. It's true as you said, Giroud still has the chance to play at Milan for a little longer, he's still good as a striker.
Age will indeed affect his physique and fitness, it will also affect his performance. But this season, Milan can expect him to play at a great level until the end of the season.
Yes, it's a little unbelievable with Giroud who is 36 years old but still very prolific in scoring goals, even at the World Cup event Giroud is still very prolific in scoring goals and that is an achievement for him. Not only that, in fact at Milan Giroud is also only one goal different from Rafael Leao who has 6 goals as Milan's best scorer so far this season for Rafael Leao.
With this very close difference, of course Milan can still play Giroud a lot longer.
Considering that Giroud's contract will end in 2023, but with such great performance and contribution, it is possible that Giroud will still have a new contract for at least the next season.
But yes, it depends on Giroud's own fitness whether in time Giroud is still very fit without receiving serious injuries. Because if even once Giroud was seriously injured or badly injured, then of course that would also be the end of his career.
It will be interesting to look forward to, because who knows and maybe Giroud will retire at the end of this season or will only play until 2023 just to complete the contract he has.