Good thread, needs bringing back to life!
I know what ftp is but I neither monitor heart rate or power. No indoor trainer either. I'm 63, 5' 6" and currently weigh 73 Kg. I'm pretty new to cycling having started in May. I was 82 Kg back then - having put on quite a bit of that excess weight over the previous winter.
Pretty much as soon as I started cycling I gravitated towards the hills. I love them even though they are a real pain.
Best I've done is a 9% average, 0.9 miles. It took me four attempts over the course of a few months. I did it but I crawled up. Easiest gear I had was 36 chainring, 34 on the back.
I think the biggest improvements that I noticed was after I started focussing on posture and breathing.
You are going to really struggle up any hill if your chest is closed in and you are breathing inefficiently. I was very guilty of that and I still need to do a lot more work on it. It's pretty hard to focus on it when you are half way up a hill and just hanging on for dear life.
I tried nasal breathing but had more success with presenting a more open chest and belly breathing. Those opera singers know a thing or two about getting air into their lungs. Then there's the off bike strength training that you can do at home. Some folk report decent gains after doing that type of training. I've just started doing some of the strength exercises, probably a good idea because I'm not getting out on the bike much because of the winter weather.