Try group rides with other folks in their 60s. When I was your age, I tested about 154 but could ride with pretty fast folks. I was maybe 3 lbs. heavier than you. On long distances I over-performed for my age. It's not all about FTP. A lot of it is about resilience. IME weight training gives us geezers a big leg up. Most of the fast folk I rode with did not weight train. The best training for actual rides which I used was thus: during the week, however much mostly Z2 I felt like doing. Weekend, one group ride of about 4 hours, 50'-70' of climbing per mile, mostly Z2 between the climbs, all-out on the climbs, say a total of 45' of Z4, 5'-10' of Z5, finish with a sprint. Group ride because I couldn't suffer that much without encouragement. The idea is to TT the course remembering that power required goes up by the cube of your velocity.

I had to lay my bike down at the finish as I couldn't dismount safely, that hard of a ride. No need for a PM. If I felt strong, I'd do a moderate group ride the day before the hard one, the hard one being aways on Sunday. You could go by HR, but going by breathing works just fine. Nice to have a record of HR and/or power though, so one can detect progress or the reverse.

There's nothing like a group ride with folks who are faster than you to get your numbers up. I'd tell riders new to the group to "hold their wheel until the blood started from their eye sockets." You want to ride with folks fast enough to drop you and then finish the route solo, which would mean a known route or having it loaded in your Garmin. I was a cruel SOB, but cruelest to myself. Needless to say, this is not everyone's cuppa. The rewards however were substantial.