Tim,

Exactly!

Suppose the case of my friend, who is born on May 11th, 1993. On their 18th birthday, the system using 365.25 will declare them still 17 - which can get them into all kinds of trouble depending on how they choose to celebrate legal drinking age (in Australia).

On the other hand, someone born on Feb 29th, 1992 will still be considered legally 17 on Feb 28th, 2010, and shouldn't be able to go drinking that day (or worse, be tried as an adult for some crime).

This is why using the YYYYMMDD method works best.

20110511 - 19930511 = 180000

20100228 - 19920229 = 179999

datediff(day,'19930511','20110511') / 365.25 = 17.998631

And Lynn's method declares the leap-year person to be 18 on the 28th.

Anyway - I think we all agree that 'age' can be awkward if the method for calculating isn't great.

Rob