The difference between the dates in years

[Alexander Zhirov via Digitalmars-d-learn]

Is it possible to calculate the difference between dates in years 
using regular means? Something like that

```
writeln(Date(1999, 3, 1).diffMonths(Date(1999, 1, 1)));
```

At the same time, keep in mind that the month and day matter, 
because the difference between the year, taking into account the 
month that has not come, will be less.

My abilities are not yet enough to figure it out more elegantly.