well being a cat 5 racer
are you talking in america doing criteriums?
dont forget theres many different types of races
your not even close to to old
infact theres 60 year old men and older then race in masters catagories
check local cities, call municipal buildings and such search for events as much as you can
realise when you do train enough for your first event
your going to suck :D
it happens to everyone
get out stretch eat right get a good ammount of sleep ride hard train hard and rest even harder
as for uscf certifications and such you can usually get a one day race license just to try it out
but really train for it
pick an event for next spring and train untill then
find out how the course is and train so you can do it forever
dont overtrain
let yourself recover and really just have a good time
at 37 your not gonna become a pro and ride le tour
but you can still win some definate money
at the national criterium championships this year the guy who was leading the pro race after halfway won $1000
just for going 50k faster then anyone
thats about 31 miles btw
theres all sorts of little incensitives for doing well other then just feeling good
find some people to ride with and do the best you can