There's a bump in speed/power that comes from mass start racing that you can't get anywhere else. Even pros that miss out on racing (typically due to injuries or suspensions) take some time to get back up to speed. I don't know why racing helps but it probably has to do with the motivational factor, both from a "I just need to hang on one more time" or "If he can do it so can I".

Racing is probably going to feel easier than a full on century assault. You'll definitely be more tired after a century, but an hour or two of racing won't leave you exhausted the way a century leaves you. There will be times in the race when it is much, much easier than a solo ride. There will also be times when it's incredibly harder. It's those harder bits that go a long way towards making you faster in general. When you realize that 30 mph for a minute is kind of normal then 30 mph doesn't seem like a sprint anymore and 20 mph seems sedentary.

Some random thoughts: my wife and I have a tandem. She isn't comfortable descending at more than about 40 mph on it, but on the flats she's okay going 45+ mph. I've been riding all my life but I'm petrified on a motorized two wheeler (moped, scooter, motorcycle) once I hit about 30 mph. On a bike that's the speed on a normal flat road in a crit, and if I was trying to bridge a small gap 30 mph means I have a flat tire. On descents I'm okay at 50-55 mph (recently), 60+ mph (I haven't hit that in a long time). I bet you'll find that pedaling 35 mph on a flat road is totally comfortable mentally speaking, even if it's a bit nerve wracking right now on a descent.

Re: crashing - I'm about the most risk averse person I know. Seriously. I have second and even third backup drives for my data, multiple computers, even multiple UPSs. I stop at stop signs and stop lights, whether on my bike or driving a car (in a group I follow the group, but if I'm leading the group, we stop). I have fire extinguishers in all my cars as well as in different parts of my house. I have hard wired and battery smoke detectors in the house. I am conscious of stuff around my feet whenever I carry my kid (4 months old) around, I plant my feet securely on things like stairways, and I try and plan what I'll do if I fall while holding him. I have three generators, one that can be plugged into a transfer switch in the house, two others identical to each other. I have a secondary heater that doesn't require more than 400w to run and it heats the whole house. Our three cars have separate wheelsets with snow tires on them because snow tires work better in snow and on ice. I keep 200mi worth of fuel in the garage (5 gal and I regularly use/replenish it to keep it fresh), and I haven't sold our third car, even though we don't use it, because it runs and it would be fine in an emergency (and it has a fire extinguisher in it too, as well as jumpers and some other stuff). Etc etc etc etc. I don't think I'm paranoid, but I definitely try and be prepared for any foreseeable and realistic problems.

In cycling I have two frames that are basically set up the same. Same (custom) geometry, same components, and they share 3 sets of wheels (not two, three - the third is a back up in case I have massive problems with the first two sets). In the household all our bikes are Campy 10s, at least in the shift/brake lever, even the 9s Shimano tandem. This way I have 4 sets of shifters to draw from as well as many derailleurs and such. We have 5 sets of Look Keos so I can use another pedal set if I have a failure. I bring extra cleats to a race, and I have 3-4-5 sets at home. I even have extra helmets, shoes, a backup set of pedals and shoes (3 sets pedals, 1 set shoes, and multiple extra cleats).

I am saying all this to illustrate just how risk averse I am. Because I'm so risk averse I insist on doing criteriums. They are the safest races for people like me.

I have consciously avoided races that hit speeds over 45 mph (except in a sprint) - no major descents for me except on group or solo rides. This leaves only crits (I'm terrible at time trials so I only go to them to help work them).

I really don't like crashing. I know it's bad, even ones where you recover fully. My thoughts on crashing and not crashing:

How I judge if someone is ready or not:
http://sprinterdellacasa.blogspot.co...-crashing.html

Avoiding crashes in general:
http://sprinterdellacasa.blogspot.co...g-crashes.html

Your advantage is that you have a lot of life experience. You have certain priorities. Other things are not priorities. Therefore you won't find yourself well over your head, like diving on the inside of a hairpin on a descent while trying to slow down from 60 mph. You'll be able to enter a crit, spend some time at the front, spend time chasing down breaks (launching them makes for slower efforts than chasing them, and you're in it to build speed, so chase, don't launch), then recover while sitting in at the back.

Get your 10 finishes in, upgrade to Cat 4, and sit on the back of some Masters races. If the San Diego area is any indication the M50+ races will be close to Cat 1-2 level in your area. You'll get plenty of speedwork in. Expect to last a lap or two of your first race unless you feel okay trundling along at 30 mph in a pack (with peaks of 35-38 mph).

Around here some of the best racers are M55+. They can win Cat 3 races, they can place top 20 in P-1-2-3 races. Age is not the limiter here, it's skills, tactics, and experience. Bank on your experience, work on your speed, and you'll be (safely) hooked.