You don't need to use a CTimeSpan object to do this, you can just use two CTime objects and get your age by using the GetYear(), GetMonth() functions etc.
this example is only accurate to the month but you can modify it to be accurate to the day and it should give you an idea of what you need to do:
CTime now(CTime::GetCurrentTime());
CTime birthdate(1972, 5, 28, 0, 0, 0);
int age = now.GetYear() - birthdate.GetYear();
if(now.GetMonth() < birthdate.GetMonth())
age--;
hope this helps
CMR