Carmelo is already 37 years old. I doubt he has only 2 or 3 seasons at most left in his career if he still performs well enough.
First, forget about the age as even Lebron James who is already 36 years old or 1 year younger than Melo, is still expected to play more season as he showed that he did not slow down, he is still dominant and getting smarter.
But it will be hard for him to get the minutes with the likes of really good players in the squad. Lakers already have Lebron and Anthony Davis in PF position, so Melo won't be getting the minutes as he used to get in the p[ast. But whenever he gets those minutes, he will convert them into scores and assists.
Melo will earn his minutes, if he plays good basketball, for sure he will earn more minutes than he played with his old team, I believe that there's a big reason why the Lakers sign him off, aside from being a friend of Bron.