Adult piranhas can grow from 6 to 24 inches in length, depending on the species. They reach this length in 12 to 14 months. A common species, the red-bellied piranha, can weigh up to five pounds and live as long as five years. Adults will spawn at around one year of age. read more
I've had a piranha for 8 years now and he still eats as actively as ever. I've also heard that they can live up to 10 years. read more