I rode 55 miles at 18mph on my third serious ride today, would i be a good cyclist?

How did you come up with the 18 mph figure? Got a bike computer that tracks all your activity - or just roughly timing it? Those who have a computer will usually add every little extra bit they can. Example: Today I rode 55 miles at an average speed of 18.28 mph. Or they'll track it on Strava - maybe Map My Ride.

Your quote, "I think what i meant to ask was if i had potential." The ONLY way to know if you have potential or not is...join a local cycling club! Your local bike shop should know of at least one. Nearly everyone has some kind of potential. I have a friend on F/B in his late 50's that just started racing CAT 5 last year. His average speed in criterium races (closed loop) is around 26 - 27 mph. And he has yet to win. But he still loves it does it every chance he gets.

If you want to race, you'll need a license. Everything you need to get started can be found on the USA Cycling website. https://www.usacycling.org/

License - https://www.usacycling.org/usa-cycling-license-information.htm

Find a club - https://www.usacycling.org/clubs/

Good compared to whom? Compared to me, you're pretty good, but I just ride for fun & fitness. Compared to any pro, you're small potatoes.

That is pretty good but you want a cyclocomputer to keep track of your distance, time, and average speed it is far more accurate.

Get a Schwinn 12 function or the Bell F12 they are the same thing and cheap for what they do. Walmart has them.

http://www.ebay.com/sch/i.html?_nkw=schwinn+12+function+computer

You are a good cyclist if you can ride 55 miles in one day. I have never rode more than 20. Are you good enough to compete, and win, no. you are about 13 mph shy of what it takes to win. You could do it for fun, and no one would be hurt, you will even be better off for it. But you can not win if 18 mph is your best speed

Yes, that is a very good ride.

Soccerref

I was 15 when I did my first 50 mile ride, my pace was right at 18.5mph, logged in by strava and garmin edge 510! Yes everyone has potential, go to your local bike shop!

If that is true and you did not ride downhill most of the way or have a strong tail-wind then you are indeed amazingly fast. All sounds highly unlikely.

55 miles is a good distance
18 mph is so fast that i doubt it was measured right
get a real bike computer, they are cheap
or enter some races..
wle

Downhill?