Conversation with Jen the other day:

J: … Dog years, what are they all about, then?
R: How do you mean?
J: Well, who decided that one human year is equivalent to seven dog years?
R: Probably the same person who decided that the queen should have two birthdays.
J: It doesn't make sense.
R: Did you know that racehorses all have the same birthday: 1st January?
J: Why's that?
R: I suppose it's to define an easy cut-off date when deciding which horses are allowed to take part in certain races—for example, a race for three-year-olds. It'll be a bit like the 1st September cut-off date they have in schools to decide which year you should be in.
J: OK, I suppose that makes sense. But is it just dogs who have their own types of years?
R: I think cat years are probably the same as dog years, and I seem to remember Paddington Bear has two birthdays, just like the queen.
J: But what about giraffes, say? Can you measure stuff in giraffe years?

An excellent question! Well, I've done some research on the internet, and it would appear that the giraffe year has never been properly defined, so why don't I do it right now?

1 giraffe year = 117.8331 mean solar days = 0.3226 human years = 2.2582 dog years

So now you know.