Cannot give a spot-on timetable for the movie, or actors (only inclinations). I'd wager late 80's, early to mid 90's. Definitely not 2000+. The main character is a Max Von Sydow or Christopher Plummer type, though I don't know whether the character is played by either of them.
Plot is as follows, as best as I can remember it: A dying composer (or conductor) has his life extended supernaturally by an assistant (I don't know how subtle this is), but he's able to resume some great, unfinished work as a result. I think the composer has a wife, I certainly know there's an older woman he's on close terms with, but he has a tryst with a younger woman, which eventually leads to a pregnancy. Ultimately, the assistant gets hospitalized because his life force is so taxed, and the composer/conductor performs his opus in a theater hall. At the conclusion of his performance, he finally dies.