My first race after I started running properly aas a half marathon, in which I ran 1:19:34. You are significantly faster than I was, so you shouldn’t have any trouble running under 1:20.
I trained from about the beginning of April - end of September, but I was basically starting from almost nothing. I had run a little bit in high school (18:3x 5k), but hadn’t really run int the following 5 years. I started by getting a mileage base, so something like:
Monday: 4-6 miles
Tuesday: 4-6 miles
Wednesday: 6-8 miles
Thursday: 4-6 miles
Friday: off
Saturday: 3-5 miles
Sunday: 8-10 miles
This put me at ~30-40 miles per week. So far as I remember, this mileage was all run at a fairly easy pace for me back then, probably 7:30-8:00 pace, maybe slower.
I then started introducing workouts. I ran with a running club and didn’t keep a training log back then, so I can’t exactly remember everything, but we did speed sessions on Tuesdays and tempo sessions on Thursdays.
Monday: 4-6 miles
Tuesday: club speed workout
Wednesday: 6-8 miles
Thursday: club tempo workout
Friday: off
Saturday: 3-5 miles
Sunday: 10 miles
I came home that summer, and then stated keeping a training log.
I upped my mileage one final time so my training looking something like this. Worth noting I had become fitter and so my easy pace was now 7:00-7:30:
Monday: 8 miles
Tuesday: speed workout
Wednesday: 8 miles
Thursday: tempo workout
Friday: off
Saturday: 4-6 miles
Sunday 10-14 miles
Tempo workouts:
8 x 1 mile W/60 in 5:45-5:55
4 x 2 mile W/2:00 at 5:50-6:00 per mile
3 X 5K W/1:30 at ~6:00 per mile (I remember this hurting really badly, and actually I cut it a tiny bit short)
Hard 10K tempo, quickest 36:35
Hard 10 mile tempo, fastest 1:02:xx
Speed workouts:
6 x1 mile W/ 3:00 at 5:30-5:40
10 x 1K W/2:00-3:00 in 3:18-3:25
12 x 800 W/3:00 in 2:34-2:38
20 x 400 W/60-75 in 72-75
I remember doing one progression long run, eg. 8 miles at 7:00-7:30 pace, then 6:50, 6:40, 6:30. 6:20, 6:10: 6:00 which is just below race pace. My longest long run was 16.5 miles/about 2 hours. That was probably overkill.
I did a 3 week taper before my race felt good, if a little nervous, on race day. My spits were:
6:03, 6:02, 6:00, 6:00, 5:58, 6:04, 5:51, 6:14, 6:09, 5:56, 6:10, 6:11, 6:06 and then change for the finish. I pushed a bit too hard up and down the big hill mile seven and then flagged miles 8-9. Pulled some time back mile 10, then just tried to stay on pace the final 3.
I hope this gives you some pointers. Best of luck.
TheBanaman