current half time to new sub 1:40 or better half marathon by December?

Get used to running consecutive weeks of at least 40 miles. Once you start finishing your runs faster naturally, you're ready for workouts. Try 12 weeks or more at 40-50 mpw with 2 workouts per week and one longer run.

Workout 1. I'd recommend one tempo/threshold run of 4-5 miles in the midst of an 8-9 mile run. For a sub 90 half, you should run the tempo/threshold portion at 6:45-6:50 pace. Maybe alternate weeks with a hill workout.

Workout 2. Intervals of some type or Fartlek. Total length of intervals should be 8-10% of weekly mileage. I prefer 800 repeats (5-6) with a 400 jog recovery or a 1200-800-400 ladder workout, with recovery jog equal to half of last interval. I usually run 800s at 5k pace to slightly slowe. Mile repeats also work, but at such low weekly mileage and slower paces I don't think they're as effective.

Long run. Work up to 14-15 miles, but 12 is probably sufficient.

Other runs should be easy mileage with strides sprinkled in.

Good luck. Sub 90 is a solid goal. That said, once you hit it you'll be amazed how slow some of the other sub 90 people look and be motivated to go sub 1:25. Happened to me.

I'd also add that your long run pace almost doesn't matter. Run easy enough to get it done without tiring yourself out for the other workouts. If you need confidence, run the last 2-3 miles faster. If I can close my last mile of a long run at half marathon pace then I know I ran the rest of the workout easy enough.

Late 20's male

165lb - what height? That's good if you're 6', trouble if you're 5'5"

1:30 is pretty decent. I have a bunch of male friends who probably couldn't ever get there. It might be possible, but it's doesn't matter. Goals are good, but you don't know enough about your capabilities yet.

I suggest a very basic approach. This is a simplification of the Jack Daniels training method - if you like reading about this stuff, buy "Daniels Running Formula" and read it. If not, just follow my plan. It may not be 100% ideal for you, but it's at least 90% ideal for anyone, and shouldn't get you hurt.

This ONLY applies to the first year of running, and is designed to build up your legs to handle running fast. It just takes a long time - don't rush it!

1) Pick your VDOT with this tool. You are currently a 38. Write down the E/M/T/I/R paces associated with this VDOT. (VDOT is a somewhat arbitrary number that gives useful training paces, and can be used to estimate performance potential at other distances). I expect that 38 is a bit low for you - if you want, run a mile time trial on the track, and get the VDOT from that - then average the two. (If the mile gives you a 44, then you'd use 41 to pick training paces)

2) Run 6 days per week. Split it up as follows:

- 3 days easy (between M and E paces - no faster!) with 5x strides* at the end

- One day that's 1/3 of your weekly mileage

- One day with 10min warmup, then 10min at T pace

- One day with 8x 2min at I-pace, with 1min rest between intervals.

3) Build mileage by 5 miles/week, bumping it up on the first Monday of each month. This will take you from 20 to 40 in 4 months.

4) Every month, run a 5k race instead of the I-pace session. Plug your time into the calculator and adjust training paces accordingly. Never adjust backwards due to a bad race - just stick to the same paces if you don't improve one month. Never run faster than your allotted paces!!! That's what race day is for.

*strides are accelerations, where you start at easy pace, and ramp up to a pretty fast run (near-sprint), then back down. I like to count 12 breaths to time them, but 15-30 seconds is about right.

I guarantee success with this, or your money back!

You want to go from nearly 9 min/mile down to 6min52/mile in 9 months?

Truly ambitious!

Can you run even 800m at 7min/mile pace at the moment, because if you can't I can't quite see how any amount of miles will see you progress that rapidly.

I'd not over-reach - all of the advice on this thread is sound as to how to improve, but with only 1 HM under the belt and one short training plan, it would be nonsensical for anyone to be predicting that rapid rate of performance improvement without knowing more about you.

I'd say follow the suggestions in the thread, book a couple of HMs or 10ks in the next few months running into the autumn and see what that tells you.

Don't expect miracles. But do expect that you can be sub 90 in the next couple of years if you stick at it.