I am a little puzzled with your original post. For my last commute to work I averaged 20 mph for 1:15 hr on a very flat route with a little bit of wind. My power meter measured an average of 250W, and I think my FTP is somewhere in the 280-300 range. If you are also doing 20 mph 1 hour solo rides, I estimate your FTP to be at least in that same range, unless your 1 hour ride was on an indoor track, flat with no wind and no need to ever slow down.

I weigh 180 lbs, but for you with 158 lbs, a FTP of 280W puts you at 3.9 W/kg, which puts you way way past beginner level. It should be enough to compete in the Cat 3 races and you should not have any trouble keeping up with all but the people racing in the Cat 1-3. Do you know if the person you are trying to beat is indeed racing at these levels?

My 20mph solos come at a big effort on a flat route with a only a couple 4% 20sec hills and little wind. The person I mentioned raced at 23.8mph for 55mi recently (talking about beating him was more of a joke than anything).

I am a beginner to cycling, but was a highly competitive runner a few years ago competing for a major university. I was in that ambiguous category below professional but well above even dedicated recreational runners. The aerobic base seems to have carried over somewhat, the muscular endurance has not.

Are you riding a TT bike by the way, because then you should be able to do the 20 mph with a little less power.
Anyway, to become faster you probably should be looking at intervals and you already found the page with the recipes. So maybe start with the 10 minute intervals, then go on with the 20 minute ones and later experiment with some of the others.

No TT bike. I'm on a $650 trek. I'm just cheap and it performs well enough. I think if I do any upgrades I'd rather have a power meter on this cheap bike than a just a $2000 bike.

I agree, I'll keep it simple to start with as far as training.