About from the age of 10. Get in touch with your local state cycling federation. It starts at about under 11's right up until however old you may be! all you need is a bike and a club or state cycling group that holds races. Professional riding is a different story though. Your country chooses you to be in pro cycling teams. So you have to be good enough before you ride in the Tour DE France!!! :) I personally race on the velodrome and road race at the age of 14 in South Australia. It's great fun, it keeps you extremely fit and healthy and it can be totally for enjoyment sake. :) Hope that helped!
Crowley Road Race was created in 1976.
Falmouth Road Race was created in 1973.
Peachtree Road Race was created in 1970.
Bol d'Or cycle race was created in 1894.
Bol d'Or cycle race ended in 1950.
Main Divide Cycle Race was created in 2003.
Cape Argus Cycle Race was created in 1978.
Around the Bay Road Race was created in 1890.
Nos Galan road race was created in 1958.
Ice Breaker Road Race was created in 1980.
Archer Grand Prix cycle race was created in 1956.
Do not cycle on the road