There’s a long(ish) thread inhabited by those of us over a certain age - https://www.trainerroad.com/forum/t/whos-over-60-y-o-and-using-tr/28280/54 that might have some insight 
I’m a couple of weeks off my 63rd birthday. I’ve been with TR this time around for 2 1/2 years. General history is of a lifetime of endurance orientated sports - running, mountaineering and latterly cycling. Only really took the latter up full time about ten years ago when my hip started playing up and running was too painful - ended up with a replacement hip inserted 9 years ago.
Here’s my FTP history:
That’s a 23% improvement. 
Or put another way - what was once my VO2max power level is now threshold. Done a mixture of TR’s traditional Sweet Spot plans, last summer using the Polarised Plans then moving onto AT managed SS plans.
Remember that FTP isn’t the only metric, there’s other things like TTE and even HR at particular power outputs that have improved. AT has helped a lot with cramps - I was getting them daily but don’t seem so bad now.
At some point my Maximum Recoverable Dose will fall beneath my Minimum Effective Dose and I’ll begin the long slow decline. Not sure when that will be though.