Sarah wrote:

> Simon, you ask if tvá vetr can mean two years. Yes, it can. I think I'm
> right in saying that an animal's age is usually given in 'winters' but a
> person's age in ár / years.

In the old language winters are the norm for people and cattle alike.
Nowadays we mostly count in years. For example in the Icelandic text
to the birthday song. When I turned three years old this was presumably sung:

Hann á afmæli' í dag!
Hann á afmæli' í dag!
Hann á afmæli' 'hann Haukur!
Hann á afmæli' í dag!

Hann er þriggja' ára' í dag!
Hann er þriggja' ára' í dag!
Hann er þriggja' ára' 'hann Haukur!
Hann er þriggja' ára' í dag!

I indicated which vowels are dropped to get the right amount of syllables
for the notes.

Kveðja,
Haukur