I’m sure that for 4 days you’ve been inundated with tales of improvement over 40.
I’m another one. So I guess I’d say this. 41 isn’t old, There are pro cyclists that old. The current women’s olympic time trial gold medalist won in 2016 at (nearly) 43. I started cycling older than you are now.
The great thing about starting late is as you age you can continue to get better for quite a while. If you start at 15, by your 40s you have to work extra hard to hold on to what you have. 
My ftp has bounced around a bit, but at 46 it was probably 375, ( I was also riding 12k a year), right now it’s down to 325 (covid playing hell, but trainerroad has me climbing back (up from 280 in july).
So let me just say, that by the time I’m 50…I’ll definitely have that 350 (7 months from now).
Keep at it.