@Rich: Your question isn’t silly by any means. There are few among us considered “gold star” for only having ever been with someone of the same sex. In fact, the first sexual experience of most LGBTQ+ people is with heterosexuals. This is changing, of course. Along with it, greater LGBTQ+ acceptance and shifts in people’s sexual behaviors.
No two bisexual persons are alike, nor are their lived experiences similar, so there’s not a one-size-fits-all. Some bisexuals date or have sex with one gender at a time, both at the same time, or one exclusively, if they have a life partner and may practice monogamy. I’m saying this to suggest that, at face value, it might be hard to uncouple your current situation without knowing if you are entertaining both genders for now or possibly transitioning. Your age only indicates that perhaps you’ve been suppressing this part of you, as the average age is much younger.
The most recent data available from the General Studies Survey shows a rise in bisexual behavior in the U.S. Operating since 1972, this study showed a doubling of the number of men who report sexual experiences with both women and men from 1990 – 2014. This is not the same as saying there are more bisexual men. More, it’s saying that men, like you, are liberating themselves and exploring their sexuality. A similar growth is also seen among women who have had sexual experiences with women and men.
Yet, having sex with both women and men is not the same as having an attraction or being bisexual. Sure, it’s possible to get and maintain an erection, but desire involves more complex psychology.
The Institute of Bisexuality uses The Klein Grid, which offers an interesting way of uncovering one’s sexual identity. It compares such factors as your attraction, behaviors, fantasies, preference and identity against your past and present behavior as well as your ideal situation. You might find it a bit facile, but it can be used to self-assess to get some more insight to better understand yourself. Short of this, the best way to know your true sexual identity would be to consult a therapist with experience in bisexuality, if this doesn’t become clear with more sexual experience with men.