Master means simply that you are over 30 (sometimes 35) and not a pro. I'm 35 years old, a Cat 1, and I do master's races fairly often. That's probably not the kind of rider you want to line up with in your first road race - pretty intimidating.
When master's races are split up by category, it's sandbag central. There isn't really any pressure to upgrade if you just do master's racing, and there is a USCF age exemption: once you reach a certain age, you get to race a category down. Ouch. No matter how you slice it, if you do an old guy's race, you will be racing some damn fast folks - especially in California. And at Sea Otter, they will be taking it pretty darn seriously.
One thing I do need to say (in response to a previous post on this thread): I firmly believe, in road racing, if you are off the back, by yourself, you aren't racing. You may be having a fine time, you may be gaining valuable experience, but you aren't in the race anymore. (I've been in this position more times than I can count, believe me.) In most races, you won't even be credited with finishing if you aren't in spitting distance of the last big group across the line. This is VERY different from the multisport world, and this is why road racing is categorized.
Why do I say this? I think a lot of people don't get it, and it's important. The whole idea in road racing is that it's a team sport, it's a group sport, and to really enjoy it, you owe it to yourself to understand and embrace this. This is why road racers need to start out as a cat 5 (or 4, for the women), always, and move up, till they find their (dis?)comfort level.
Find a local road team, and do some group rides, with roadies. They will let you know what the best races are to start out at, and which ones to avoid (and there are always races to avoid.) I strongly, no, urgently, recommend getting plugged in to the local roadie rides before you start racing. Riding in a pack, in race conditions, is not something you want to learn during a race, especially since you probably have way too much fitness for your own good; your strength to skill ratio is going to be way out of wack when you start road racing, if you are even a moderately good tri rider. This is where all the roadie "triathletes can't ride" prejudice comes from, I think. It's also why any local cat 5 team would love to have you aboard.
Road racing is incredibly good fun, but there is a steep learning curve. Start out at the very bottom, and go ride with the local roadies. They WILL help you, and you owe it to yourself to go into this with the tools you will need to succeed, and more importantly, have fun.
Good luck,
MH
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