[@KatherinWinter]
Your intro post said that they've been around for "a few years". I've always identified a few as being 3-5. In Alyssa's bio, I was going to have her have had an incident in middle school that attracted MiB's attention, so, keeping a file on her and her strange ability to stop what they assumed was an extraterrestrial force, they kept an eye on her. When they created BoSA, they extended a job offer to her, both for her abilities, and for her experience as a private investigator, which is what she did for a few years after she dropped out of high school.