I think you have to try relationships with both men and women to find your true self. Sexuality is a question that is answered by experience and not thought. Finding the answer will mean taking risks. You also seem to have a black and white view of things - being either gay or straight. There is a possibility you might be bisexual. Regardless of whether you are gay, straight or bisexual, the important thing is to find the right person, someone who loves you back as much as you love them. It doesn't matter if they are your age or older. All that matters is that both you and your partner are happy.

It sounds like you have a lot of conflicting feelings, e.g., a need for sex but feelings of disgust / dirtiness afterwards, and would benefit from talking your issues over with someone. A therapist could help with this.