[Solumina]

You can id as both, older people tend to self describe as bisexual just because that term has was around when they realized they weren't monosexual (attracted to just one gender) and pansexual is a much newer term. There are a lot of people who say that bisexual means that you are just attracted to men and women and that it is trans-exclusionary but that isn't necessarily true when I use it I mean that I'm attracted to people of my gender and not of my gender those are the two categories that the "bi" refers to and that usage is pretty common in the bisexual community. I also usually just use the word queer in casual conversation because it is a broad umbrella term and it hasn't been eroticised in pop-culture to the extend that bisexual and pansexual have been.

In short just use whichever term you feel comfortable using, you are the one who gets to define your own sexuality.