I'm 23.84654477422623 years old. That's 8709.9888425926 days old, or 8709 days, 23 hours, 43 minutes, and 56 seconds old.
According to my birth certificate, I was born 9:42 PM, July 19, 1989 (CDT); that's 2:42 AM July 20, 1989 (UTC), Julian date 2447727.6125. This page is generated by a PHP script that 1) grabs the current Unix time from the server and converts that to the integral part of the current Julian date, a.k.a. the Julian day number; 2) calculates the decimal part of today's Julian date, which is for some reason not provided by PHP's unixtojd() function; 3) finds the number of days between these two Julian dates, a.k.a. my age, and outputs it as number of days + number of integral days, integral hours, etc.; 4) outputs my age in years.
4) is a little complicated since the length of a year varies. I was born in 1989, I probably won't live until 2100, and 2000 is divisible by 400: therefore, every year in my lifetime divisible by 4 is a leap year. I was born in 1989, so there were 365 days until my first birthday, another 365 days until my second birthday, but 366 days until my third birthday (since we cross over Feb 29, a leap day, in 1992, a leap year). Therefore, each year of my life equal to 2 mod 4 will contain 366 days and all the other years will contain 365 days. I use this rule to determine how many days have elapsed since my most recent birthday.