Same answer, really. Do specifically botto's short "how to race" thing. Find a group ride. When you outgrow them, find a faster group ride. If there are racers in your group ride and you're mixing it up with them, that's good.

Bike racing is based around drafting and therefore tactics. Running - if you start at a 5:30 pace, a 7:00 miler won't be able to stay with you long no matter what. But in bike racing, if you start time trialing at 30 mph, and I'm on your wheel (23 mph time trialer), I'll be there after 10 or 15 or 20 minutes, and I'll be pretty fresh. Drafting is amazingly powerful.

As a trained runner I'm sure you're strong aerobically. In fact I'm sure you're much stronger than me aerobically. That means very little until the road goes uphill, you're in a TT, or you're in a break, all of which significantly negate the draft. Until then you're at the mercy of us wheelsuckers, those that benefit off the strong guys' work.

I just posted a clip about Somerville. A Cat 2 race, I averaged under 180 watts (I think under 160 actually) until the last lap. At the beginning of the clip you'll see us soft pedaling and coasting while going 30-32 mph. Someone strong is at the front, killing themselves, putting down probably 500-600 watts. We're sitting in enjoying life, averaging maybe 90-100 watts.

I have no idea what you ran in track but my fastest ever mile in my life was a 6:30 and that was 30 years ago. I die running 7:00 pace now, it's like sprinting to me. I ran 1.5 miles a few years ago for a test - it took me about 12 minutes on the track. But in many Cat 3 bike races I'm okay. Cat 2s, less okay. It's more about learning how to ride in a group, and that's what group riding does for you.

If you are a good runner (4:30 mile? I don't know what's good anymore) and you learn the tactical stuff in the first few years, and you're not a total jerk in person, you can probably turn pro, and I'm totally totally serious. If you're a absolutely phenomenal runner (4:00 or faster) and you ignore tactics, you'll be a strong and dumb Cat 2 or Cat 1. Everyone loves a strong and dumb Cat 2s. If you're in my area, please forget about tactics, just ride hard

If you want to race well for yourself, learn about tactics. The bike fitness will be there quickly, just a matter of adapting some muscles. Figure a year of riding and racing and you're done, at least that's what ex-pro Chan McCrae said to a friend of his while I was nearby.