In Moana Heihei is shown in the scene near the beginning when Moana is like 2 or 3, and she is 16 when she goes out on her maiden voyage. So Heihei is like a 13-15 year old chicken for that trip. But supposedly Heihei is in Moana 2 which takes place 3-4 years later, so that chicken is now somewhere between 16 - 19.

If there is a Moana 3, Heihei will likely be very close to being older than “Muffy” the current record holder.

(It’s also possible that Heihei is actually older than Moana. In which case he would be more than 20 years old in Moana 2)