I had some girl rant on to me about this the other night down the Old Bore (a sleazy pub

).
It's the same for everyone - and for children born after 2000 it will just come to 11.
All your doing is just working out that your birth year and your age will add up to 100 plus the particular year of this century. It's not unusual - if you do it for 2012 you will find it comes to 112.
Still confused? it's just 100 (last century) plus the years of this new century (in this case 11 years so far). That's all.
Now don't lose sleep over it lol
peace ,acid.