I just ran sub 3 for the first time at age 43. I started running about 4 years ago. I've only run 1:24 for a half once, but in recent ones was more around 1:26, but on no taper from marathon training. Previous marathon PR's were a couple of 3:03's in warm weather. Here's what I think got me over the hump this fall.
1. High quality long runs. No jogging out 20 milers, first 10 miles or so comfortable, but not "easy" pace. Second part of run 8-10 miles at marathon pace or faster, with about 30 seconds every 2 miles to break for water/race day fuel. Got 3 of these types of runs in over the course of 6 weeks leading up to the race along with 65ish miles on avg per week...
2. Six weeks out, eat as healthy/clean as possible (different meaning for everyone), focus on quality sleep. I ended up dropping some weight during this time, which for me was a good thing..
3. Race day. Indianapolis Marathon. Great course, mostly flat with just a few hills to keep some variance....and perfect, I mean perfect running weather. Average probably around 45, a little sun, little to no wind.
4. You are likely going to have to really want it after 20 miles. I was hurting, but keep going and had to still be able to run 6:50's late in the race with a surge in the last half mile to get to 2:59:23
You have a chance for sure, finish the training wisely....don't over taper, but show up rested. Win the mental battle when you are suffering. Enjoy!