You could start by first asking how many days old you are. If today at exactly noon is your birthday, and you are in the same time zone that you were born in, then you are exactly 365 x 13 days old plus the number of leap days (February 29ths) since you were born. Now you know how many days old you are.
Each day has 24 hours. Each hour has 60 minutes. If you multiply these together you get the number of minutes in a day. Then if you multiply the number of days old you are by the number of minutes in a day, you find out how old you are in minutes.
If today isn't your birthday, then you have to figure out how many days it has been since your last birthday. If you aren't in the same time zone as your birthday, you have to adjust for that as well (and you might also have to think about daylight savings time versus standard time!)
Here's a question for you: I just passed my 20,000,000th birthday (in minutes) a little while ago. My friends failed to notice and so they didn't throw me a party, but they had just given me a normal birthday party a short time before. How many years old was I for the party?
Stephen La Rocque.>
This problem provides an example of trying to apply mathematical precision to situations where it doesn't apply. It's sort of like measuring the distance between cities in millimeters -- if 100 people do it, you'd get 100 different answers.
The concept of a year is not really precise enough to work with, even though Jonathon Larson came out with a hit song "Five-hundred twenty-five thousand six hundred minutes." He assumed a year of 365 days with 24 hours per day and 60 minutes per hour: 365*24*60 = 525 600 minutes. (He no doubt chose these numbers for their rythmic quality rather than for their mathematical precision.) Our calendar (the Gregorian) averages 365.25 days per year (so 525 949.2 minutes). I suppose your 13-year period could have either 3 or 4 leap years (of 366 days) and the rest with 365 days, so maybe it's those numbers you want to use. The solar year averages 365.242216 days (for the earth to travel once about the sun), although the exact amount varies from year to year. Finally, if you happen to be Moslem, then your year lasts only 354.36667 days, on average.
In summary, to solve your problem, you must decide your precise definition of one year; then you multiply that by 24*60 = 1440 (adding or subtracting days according to how you want to deal with leap years).