I’ll define A-list as:
-Always either received or shared top billing in a movie
-Continued to get plum roles in big budget movies
-Continued to be critically and commercially successful (everyone can have a few flops, but I’m talking actors who at least most of their projects work financially and critically)
The current holder would probably be Jack Nicholson who is going strong after almost 40 years. (More than 40 years if you count Easy Rider, but I’m dating it from his early starring roles.)
For women- who generally don’t have the shelf-life of their male counterparts (not a sexist claim, just a statement of fact- women over 40 rarely play main character or romantic lead) the honor would probably have to go to Katharine Hepburn, who had a run of well over 40 years from her 1930s ingenue days til On Golden Pond.
Anyone you can think of who’s been A-list for a comparable or longer amount of time?