Green Island, Australia - Cassius, the largest crocodile living in captivity, recently turned 120 years old and he's still growing, leaving scientists stunned at his longevity!

This ginormous reptile lives at the Australian wildlife zoo, Marineland Melanesia, on Green Island off the northeastern coast of Australia.

A saltwater crocodile, Cassius stretches out to a whopping length of 17 feet and 11.75, making him the largest captive crocodile in the world – and he owns a Guinness world record to prove it!

And the most surprising thing about Cassius is that he's still growing.

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Graeme Webb helped capture the croc in 1984 and he determined Cassius has grown 13 inches in the last 20 years.

"He was a big old gnarly crocodile then. Crocs of that size are not normal," he told MIX 102.3 in Australia.

This unique case study is helping researchers gain some "serious knowledge on longevity," per Webb.

According to LiveScience, Cassius was estimated to be between 30 and 80 years old when he was captured. Guessing the size and the age of these apex predators can be difficult.

"There is no way of knowing Cassius' actual age as he was born in the wild and the age is just an estimate," Toody Scott, a crocodile keeper who looks after Cassius, told LiveScience.

Sally Isberg, managing director at the Center for Crocodile Research in Australia, told Fox, that Cassius is "a happy, healthy boy." She added, "He has such a personality. He gets called over to one side of the pen and is just happy to wander over."

Hopefully, this fascinating croc will keep living and growing!