Age 59. I'll second those who say hill reps. But they have to be done, in my experience, on a particular kind of hill, a particular way.
I've had great luck with 4-6 repeats, medium speed, up a steep hill that takes me almost exactly 60 seconds. Actually, it takes 60 second from the bottom to about 20 yards past the crest.
I warm up for the hills by running about 5 miles, with the last mile or so at tempo. It's important to do that: get the blood flowing. First time I do the workout, I'll do 4 repeats. Add a repeat each week to make 6. Ideally, do the workout twice a week for a couple of weeks after you've built up to 6.
I do NOT hammer the hill. I pick a speed that I think I can hold, and I go a little slower the first one. Get it out of the way. If I'm doing four, the third one is the hardest, and the fourth is just getting it in.
I vary leg lift. Sometimes I deliberately lift knees high and don't worry about forward velocity; sometimes I run it as efficiently as possible, like in a race.
If I'm doing it right, my heart rate as I crest, push, and finally stop, gasping, ranges from 178 to 184. 190 is my max. So we're talking hard 5K pace, but not completely maxed.
Pause to catch breath, then jog down. At the bottom of the hill, especially in the later repeats, I sometime feel as though my stride has been lengthened in an almost explosive way. So I'll stride out.
And that's it. My experience is that a longer, more powerful stride shows up almost immediately. Do 4 reps on a Wednesday and by Sunday you'll notice the difference in a faster easy pace, faster tempo pace, everything.
Do this workout twice a week for two weeks and you'll be going "Holy s--t!"
4-6 reps, 5K effort, 60 second steep hill. Once or twice a week.