And you do not have to worry about whether you are in good shape and good looking or not. Be clean, considerate, polite and most providers will be happy to entertain you.
As swim said, there are good reasons to start with somewhat older providers. They will be more attentive to your needs, take you through things more gently as you learn the ropes, and usually be more interesting to talk to, but if you want to search for that perfect cheerleader you lusted after in high school. join the club. Odds are good you will be successful in living out that fantasy.
One thing you may find with some of the younger providers is that they do not provide real GFE service, are not that into it, and have a lot more restrictions on what they will do. While that may be about you if you are stinky, rude, or otherwise abusive, it probably is just how they roll.
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