You're fast if you can beat most normal athletic people in a race. That means your softball team, the flag football league you play in, all the guys at pick up basketball, everyone pumping iron at the gym, and all the people in the local 5k.
Consider that combined group to be your competition. Therefore, I'll go with 12.5 in the 100, 5:15 in the mile, and 17:15 in 5k. Those times would make you one of the faster runners.
I would consider breaking 5 for the mile fast for a girl.
sub 50 seconds for the 400 meters. Someone who can run 14:00 for 5000 meters and not break 50 for 400 meters is not fast. Very economical, good lactate threshold,and decent Vo2 max. But not fast.
For the Marine Corps physical fitness test, a perfect score on the 3 mile run is 18 minutes. Not many Marines achieve this. It's on the same level as 20 pullups, which is also a perfect score.
Even though we at letsrun.com don't consider 18:40 to be "fast" for 5k (that's around 6:01 pace), it's probably as rare as the guy who can do 20 pullups. Come to think of it, between my friends, family, and co-workers, I can't think of more than 1 or 2 people who can do either of these.