In reply to Jon Greengrass:
One thing I forgot to add earlier was that it should be relatively easy to get to 8a by your 40th.
I had a coaching session many moons ago with Dave Macleod. He said (paraphrasing here slightly) climbing hard is pretty easy, you've just got to want it badly enough, and that's where most folk let themselves down. Everything else will fall into place if you want it and do what is required to get there.
I was probably about 40 at the time, and I gave myself loads of time to hit 8a, namely by the time I was 50. Needless to say, that came and went and I didn't tick one! But that was because I didn't apply myself, and I knew it. My partner, who was climbing the same grades as I was back then, did apply himself and yes, he got his 8a. In fact he went straight from 7b+ to 8a, skipping the in-between grades! He found a route that he liked, was a strong line, suited his strengths and was relatively local. We pretty much ditched other venues whenever it was possible to climb at the 'target route' location. I tried the route too but it really didn't suit me and (perhaps because of that) I didn't really like it as much as my partner.
Looking back at my logbook graphs, I was probably climbing the most when I did a couple of 7c's but both of them were after fairly protracted sessions on adjacent, easier routes (eg. Hamish Ted's at Dunkeld) so I knew the terrain, had the stamina and didn't need that much strength to get up them. I took days off work to go up mid-week and get on the routes repeated times, ingrain the moves, refine beta and frankly, beat them into submission. In other words, I did what was required, including training for them which involved building a woodie at home and setting enduro-circuits to mimic the routes.
I was disappointed I didn't get to 8a by the age of 50, but I'm now 54 and have more time available to train, climb and get away on trips and I'm fairly confident I'll get my first one once I've been applying myself over a longer period. That might be next year, the year after or by the time I'm 60. Your first step is to figure out how badly you want to climb 8a and then formulate a training plan that will get you through each of the 'stepping stone' grades to get you to your desired destination.
Best of luck, it'll be hard work but fun if you stick with it!