Usually I think I am fast if I am around people who are slower than me. When I go to practice and there are sub 14 guys I don't think I am fast. When I am at home with All-Americans, I think I am slow.
I won't think of myself as fast till I break 14 or 4:05y. I won't really think those are all that great and won't call myself fast until I have gone sub 13:30 or 4y
I generally don't think of 23 year old guys as fast until they have broken 14:30, and generally even less so if I dont know them.
Even so, I won't call anyone fast until they have run under 14:00. If someone asks me if someone is fast and they have run like 14:50 I say they are pretty good, but not that fast.
Its all relative, I think high schoolers are fast if they have broken 4:30, if I know them. If I dont know them, I dont think of them as fast until they are under 4:20, even though I came just short of that barrier as well in high school. I dont think I was particularly fast in high school.