After a bit of experimentation I find that zero ticks corresponds to a date of 01/01/0001.
So if you subtract birth ticks from Now ticks you will get an age in ticks that is relative to that date.
Thus if you calculate the age in ticks by subtraction, convert to a date then subtract one from each component I think you will have the age in days, months and years.
Sorry, I have not tried to analyse the code that you showed us...
Mike.