I had a good friend who ran 4:24 and then for 4:23 in the mile at age 40. He also ran 157 800 I believe. Those races were in an early part of his first indoor season in quite awhile and if things had gone better I think he would have been very close to 4:20. He had not run track in several years but had stayed in good shape and ran a lot of open track races in his late 20s and early 30s.
In high school he was a 153 800m Runner and I believe ran mid 420s in the mile but was much more focused on the 800. I think he may have run a 151 800 relay split in college but did have a few injuries.
Late 20s /early 30s I believe he ran 153 again, and a lot of 155 156 races. But then took a break from the track for several years.
He weighed exactly the same when he was 40 as he did in high school and college if not less. He started doing a bit more miles to prepare for his mile races at age 40. He had a ot of speed. Stayed healthy at that time.
So it's possible to get close. But he was a different athlete than you. it seems you probably have a much bigger aerobic engine however as many others have pointed out you will have to work on your speed for sure. This guy was extremely good in the 800 over the different periods of his life: High School, college, age 30, age 40.