How old are you?

A friend studying psychology started a Skype chat to ask some friends whether they would take part in an experiment. She was looking for people between 23 and 29 years. Here’s one response:

A: (hi)
not 23 - born xx.4.84, you’re a bit too early :D
B: 1984 is ok
A: I see
C: :^)
A: well, then I’m on board :D
C: you are 23 when you’re born April 1984
you’ll be 24 now :^)
A: I see
shit
yes
C: (shake)
A: I had counted with 24 (blush)
I think I better hide…..