It really depends on the course, a massive climbing course will be much slower than a flat or downhill course. ive heard cat5(the lowest) ride about 25mph on average on a flat-ish course. but also, this is made much easier by drafting, where youre not fighting the wind constantly. get out and get used to your bike, then as you get stronger(or even from the beginning), try group rides. just google road bike group rides in your area. group rides will get you used to racing style riding on the more advanced rides. ive also heard it takes 3-5 years to become a decent racer, but that doesnt mean you cant start earlier than that, just dont let the faster people discourage you. and dont enter a race before trying group rides. i know i would feel REALLY bad if i caused a wreck because im new. hence, no races yet. Im still trying to hit up a few group rides, but my work schedule conflicts with anything but mountain bike or casual group rides