I've no idea.
I just hope the folks are right about the number of years as I still have some left then! Ha ha.
I think it's really dependent on your CTL over those years. If your CTL is one of low intensity group rides for 6 hours a week for 6 to 8 years......only so much has been gained.
If you're doing a lot of load in those 6 hours per week over 6 to 8 years, I think the answer may be different.
I'd say, IMO, I may reach my ceiling a lot earlier than others. I'm constrained to 5 to 8 hours per week. I typically use a good amount of intensity and steady state. I don't have time for 4 hour Z2 rides. I think this year may be "it" in terms of optimizing the engine on the time I have. Then it will just be skills and moving the fitness from one energy system to another depending on the races I want to do.
How long is a piece of string? However long you cut it!