I'm aro/ace, and I figured out the "ace" part before the "aro" part. It might just have been that the queer pride group at my university had some detailed resources on asexuality. I've had a couple of crushes in my life, but I've never really felt the desire to have a long-term romantic relationship. Maybe having one or two fleeting infatuations kept me from realizing that I'm not all that interested in dating or marriage.
For me, being both ace and aro simplifies my life in some ways, but it also sometimes makes me feel that I'm missing out on a vast range of human experiences. I'm spared from the bad parts of sexual and romantic realtionships, but I'll never experience the good parts.