That's an unconventional way to write a 2-digit year, so I would expect that case to be explicitly called out in the description if that were the intent. I mean, for that matter, the description didn't explictly state that the digits are always in base-10, but you don't find my solution problematic because it doesn't handle input such as "A8F4", do you?

At any rate, I will defer to the test suite, which is the ultimate arbiter for questions such as these.

Year = 55 is not part of the input domain. See the kata description.

No, it's not a tie:

• P1: A pair with 7, 6, 4 kickers
• P2: A pair with 7, 6, 5 kickers

As the kicker 5 outranks 4, P1 loses.

See: https://en.wikipedia.org/wiki/Kicker_(poker)