Okiemike as for looking for NON-PROS especially in the 18-25 age range, I can only wish you good luck; you are going to need a lot of it (luck), and game, and money, and time, and spanish speaking and understanding, and looks, and and and and !!!!!!!!!!
I think you said you were in your 40s; most of the 18-25 chicas you meet in the malls and other upper scale places will not give you the time of day, most of the few that will are going to be hookers just out shopping, or if in a club, partying with friends. Even if you get lucky and meet a very young non pro, very few are going to just jump in bed with you within the first week. And by the time you get her there, you will have spent a lot more time and money than if you just meet and pay a PRO at one of the many venues here. AND almost always, you will get better sex, thou maybe not as romantic.
Again I am not saying you can not meet and have a fantastic time with a non pro, just that you will be very lucky if you do. Hell even an old fart like me has done it,,BUT I live here, have the time, speak the language, and kinda know what to look for.
If you go into some of the poorer barrios looking for a non pro, yes you will be more likely to fine one (they tend to be more desperate for a better life and even the non pro will tend to look at any gringo as a meal ticket); that is if you do not get mugged first by someone else looking for a "meal ticket"!!! One of the BEST places to look for non pros (poor) and more willing, is in the tiendas in the more dangerous part of central San Jose. But you have to be "shopping" for them to be able to spend any time with you in the store to get to know them; they are very often und***ge; and usually very uneducated.
As others have tried to suggest, till you have been here a few times, know the 'scene', speak the language, and have a lot of time; just stick with the venues where the 'Pros" are and HAVE FUN without all the hazzle.
AND do not worry that much about the und***ge problem; und***ge chicas is not that big of a problem in the major venues; just be careful and if she looks really young, run away no matter what she shows you. Stick with the ones that look over 20 and always remember "with age comes experience, and quality of service!!!!!! In all honesty, not always but in most cases!!
Just quit worrying, come on down, relax (now that is a very good idea), and have a great time

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Old and retired but still bang, and bang, and bang!!!
