I voted for "my whole life" but come to think of it, that wouldn't be exactly true. I remember I wasn't shy at all when I was little. My SA had developed later on, I would probably say that junior high and then high school contributed to that the most.
I was wild and hyper when I was kid but suddenly became quiet and subdued and really shy in 6th grade out of nowhere, when I was 12. That was 10 years ago. I'm only like that in public though. At home I'm still wild and crazy.
Since I can remember.
The first time I got really anxious was in kindergarten and it just grew from there.
I wasn't actually diagnosed until I was about 15, though. Before that, I had no idea what SA was or that I could have it. I just thought I was really shy.
I don't think my sa started until some point in school. I had SA by Junior High for sure. I might have had sa as early as elementary school, because that was when other kids started to pick on me. I chose "my entire life", because my sa goes beyond 10 years. It definitely has been the majority of my life.