Hello there.
The offerings are mostly Eastern European, although there are few Asians and Latin Americans as well. Western European and British escorts are more expensive, on average. Um, some of them won't see individuals of certain races. Most of them won't see blacks. Some of them have age restrictions as well, but since you're almost 30 you should be fine.
In terms of the actual experience, it varies. Are you looking at an incall (where you go to the escort) or an outcall (where the escort comes to you)? What is your budget? Are you booking one with an agency or an independent one (avoid pimped cheap whores who are doing it for drug money)?
Obviously, London has the largest concentration of escorts, but you probably won't have trouble finding escorts in smaller cities. My experience is limited mainly to central London; by the way, you should never engage in this practice near where you live or work. Go somewhere slightly farther away. You don't want the escort to recognize you in your local Waitrose.
Don't be stupid. If the escort isn't who she says she is in her pictures, get out. Confirm the type of services you want before you hand over the cash. Leave the Rolex at home. Bring just enough cash to pay her and enough for a taxi ride. And on your way to the escort, don't freak out. Don't look nervous. Act as if you belong in the apartment building/hotel lobby where you are waiting.
PM me if you have more questions.