(1) The general ways I have been made aware of a therapist is through either:
first, the decision was made for me, when I was 16 and 17. I had no choice in who and one point they had me seeing 3 people at the same time

second, when i was older and was able to make my own choices, to some extent the therapists were found through either the insurance provider listing or referrals.

(2) when I wasn't really making decision on who I saw, there was only one that I was happy with but that was bascially the luck of the draw.

when I got to a place where I was old enough to decide I did or didn't like a therapist, it was basically made via some "undefinable" connection. that has only happened once and is with the my current therapist. when I talked to her on the phone to make the appointment, i wasn't impressed. but from day one when i sat face-to-face, i felt different and like an instant connection. hard to describe how you "know" this it the one to choose.

(3). I'm 33 and my therapist is, last time i checked, 56. But I don't know her birthday so she may be 57 now.