Slow-growing or slow-maturation would have to be the Davos (the croc/aligator type people) who have a slow maturity growth. BUT! The trade off is if they can survive the process of becoming a full on adult, from then onwards their scales and hide naturally hardens over time, making elders of the Davos race being quite formidable and difficult to kill with conventional weapons.

They still have a weakness for their underbelly, but even that has been hardened over many years save for one spot on the throat that is small enough that is hard to pierce, but when something does pierce it, they can be killed.