holy crap i am not the father..i am not
Well not sure this is any help but I am 37 I started at 15 and to be honest mine has never got into a regular pattern I can be anything from 1 to 5 days late in any normal month although currently 2 days late seems to be me.
Yea. Are you under pressure lately? Or on medication?
Are you under excess stress?
Well I'd go get checked out. Just to be on the safe side. As I am not a woman, but a man. My other thought is, if you are sexually active and on birth control, this could cause some issues. Then I could be 100% wrong......and I'm sure someone will let me know.
I went to the doctor about the same age as you over the exact same thing...he said "you'll be fine don't worry about it, you might grow out of it or it is just the rhythm of your body". I did fine.