[HartleyMBaldwin]

Rosie was born in 1991 and turned 33 on June 1, which in cat years is an extraordinary 152.

Well, 152 divided by 9 is less than 17. It's not unusual for a cat to live to 17, so I guess that Rosie's nine lives ran consecutively.

[FredSchwartz]

This is the formula my vet used.
A cat is fully grown at 1 year and can have kittens.
so they consider the first year to be 16 people years.
The second year, a cat matures a great deal and it’s considered to be 8 more people years, so 24. After that, based on health issues that cats develop just like people, and the ages that cats die, they consider it 1 cat year = 4 people years. So based on this formula, 33 year old cat would be 148. So it’s close to their number.