Doesn’t need to be girls of your age group, just determine if there are any barriers. For instance, with your mother’s friend, she is married and may be committed to that marriage, and she is a friend of your mothers which may mean a great deal to her. Then think in terms of what might be going through her mind. Let’s say she is thinking of sleeping with you. This may confuse her to begin with because the feelings would be sudden and you are so much younger than she is (are there any laws of statutory rape in your country that would make you a minor?), so there’s one possible barrier, then the thought of cheating on her husband and ruining her friendship with your mother would weigh heavy on her mind, two more barriers.
Of course there are ways to get around all of this, but then you have to ask yourself, are you prepared to do that? Do you care about her, or do you just want to get laid and you really don’t give a damn about her feelings or if your actions will lead to ruining her life?
Its sort of like driving a car. You need to get from point A to point B and there are 5 different routes you can take. Some routes will lead there quickly, but may risk damage to the car, some routes will take longer, with less damage, and some will just get you half way there and then get lost with no damage. Probably a bit of a bad analogy because a car is an inanimate object, but how much damage to the car (your mother’s friend or another woman/girl) are you prepared to do.
Any magick that you perform comes with the question, no matter what the outcome, are you prepared to take responsibility for your actions. If not, then don’t do it. There was a good article I read some years back by Phil Hine about morals and in the article it said something to the effect of “If you are not prepared to stand up in front of a crowd of people and announce what you did, then don’t do it.” I think its the best guideline I have ever come across.