Thanks for coming to us with your question.
I understand that going to an all girls school can limit the interaction you experience between other boys of your age. Do any of the immediate friends you mention have any brothers close in age that you get along with and or talk to? Do you have any sisters? How old are they? If they are old enough to have boyfriends perhaps you could ask them about what you are feeling.
It sounds like this boy you met in the volunteer program was nice. Not being attracted to him sexually could mean many things. Perhaps he was not your type. The type of person that people are generally attracted to sexually are people that have certain traits such as sense of humor, common interest, and physical attraction. It could be something like he was too tall or too short. The lack of attraction you felt for him is not alarming. Throughout life we meet many people that we become friends with because there is no underlying physical attraction.
Another possibility is that since you have not talked with or spent much time with boys, that it is a new experience for you. Were you comfortable talking to him? Why do you think that not being attracted to one boy means something may be wrong? He is just one boy and you will meet many many others in your lifetime.
You talk about how after thinking about this extensively that you began to find women sexually attractive. Appreciating the physical characteristics of the opposite and same sex occurs often. Many teens question their sexuality. Some experiment, others question themselves. There is no right or wrong way to deal with the feelings you are having. You also mention that there are no girls that you have a crush on. Seeing people as sexually attractive is a way of appreciating something you find appealing. Just because you find this appealing does not mean you have to have a crush on the person.
Your dream does not sound old fashioned at all, it sounds like you know what you want. Go easy on yourself. Perhaps you will meet other boys through your volunteer work, or through friends. There is no rush to figure out life. Enjoy the experiences you are having now. There is much life ahead of you and many more people to meet.
Hope this helps, and please ask any other questions you may have.
Suzanne, for Alterheros