Josheli,
You do need Lydiard. Perhaps someone was just being dramatic.
I noticed a couple of things (being a Lydiard coach):
1. Two month-long (months: 7-9) hill phase is long.
2. You may not need a full-on hill phase, really.
Hill phase is for developing the lower leg muscle, especially type 2 and type 2B. You may be able to develop that just by incorporating a lot of hills in your regular running and having a three to four week "semi-hill phase" with hill repetitions. The pogo stick, bounding, and similar drills can be quite damaging for a 50-year-old. Also, the power developed from the hill phase really benefits middle distance runners more than 5,000m+. Although you will benefit from doing some sort of hill phase, I would use a little caution (consistency in training is almost more important than specific workout outcomes).
I would use the schedule you wrote out as principles rather than as a schedule. Or as a template. Adjust daily by how you feel.
Sub-20:00 5K at age 50 is 73.83% age-graded performance, which is pretty good. That equals 17:32 open performance. Sounds like your goal is spot on.
Anecdotally, in my experience, so far, it takes a while to re-develop fitness after a prolonged break. You know how people say, "it is easier to get fit on a comeback than it was the very first time"?
I think there is a statute of limitations on that. I had a decade off for three surgeries....
Back for a full-year, plus and the gains from this work is obvious and measurable, but it is taking some time......be consistent, enjoy the base phase, but instead of having a set date when you will end the base phase and move to hills, try this:
Weekly or every 10 days or so run an out and back effort on the same route each time at exactly the EFFORT (not pace - don't look at watch). Warm-up and warm-down and then run 30-minutes out as hard as possible without straining. Don't go to a marker, go to 30-minutes. Don't run for 30-minutes back, run to where you started from and you should see a small negative split if run properly. You should get faster on this effort, but eventually, you will see diminishing returns, THEN is when you want to move onto another phase. Some people respond quickly and some take some time to stop improving.
Alternatively, you can do the same thing but to a marker, each week. At roughly the same amount of time....the fitter you get, the further you will go past the starting point on the return.
The purpose is to put good pressure on the cardiovascular system for a sustained effort without straining. Don't race it. Racing in the base phase is like pulling up a sapling that you planted to check to see if the roots are healthy, killing the tree in the process.....
In the age of Strava it is almost a paradigm shifting effort. I have had to explain this thing half a dozen times to some people, who, for example, will look at their watch while running and then report, "oh yea, I was running 4:30s for X amount of time, man." Or "I tried to get to 4:10s...."
On that out and back run, that is completely defeating the purpose. You should finish and wonder what pace and time it took on the return and THEN look at the watch.
Done properly it is such a wonderful AT stimulus run.
Cheers,