No one doubts Modric's quality; he's one of the best midfielders in the world. However, his advancing age will significantly impact his performance and physical quality, so I believe his contribution is somewhat less than optimal.
There's no definitive proof for AC Milan, but I've seen the arrivals and departures of several players in their squad not make them stronger, so I'm a little pessimistic about AC Milan.
Modric joined AC Milan as he knew that Serie A is a league that matches his old age and his skills. In addition, joining AC Milan will give him more opportunities to play while a next summer in 2026 will be time of World Cup 2026 which is his last tournament for his national team Croatia. Modric has many reasons to focus on his training and playing with AC Milan as he knows his time is counting down as a player at a club and at his national team.
Modric has given out all his best in Real Madrid, and there's nothing much he can do for Milan in his current age. I don't like the kind of players Milan are signing this time, I feel they are not that strong enough to take the club far. Rumors are around the corner that Milan is interested in signing Jackson and Gnarcho. I wonder what they see in Jackson that they want him.
It's true and he is very old now but he will be able to contribute something for AC Milan with his skills, experience, professionalism. At his old age, he will have limited playing time for AC Milan but every minute he plays for them, he dedicates his energy and focus for his performances and I believe that he will be very helpful for AC Milan.