I'll take this at face value, but you've opened a pandoras box on yourself!
There is no correlation between age, or price you pay. The most expensive wg in the world could catch something tomorrow. Similarly a £10 street walker could go her entire life without catching something.
In terms of race, to generalise i'd stay away from EE, South Americans and Africans. They aren't as developed in their attitudes towards STI's. Happy to duck for cover as I get accused of racism or some such but my opinion.
In short, it sounds like you're already wary. Why not try a massage with a happy ending or similar?