Adam possesses the ability of rapid cell regeneration. Like Claire, Adam is sometimes unable to regenerate if an object is inside of his body until that object is removed (Lizards). Adam initially appears in 1671 as a man in his late twenties to early thirties, and seems to be able to survive for hundreds of years without apparent aging, as he has a similar appearance while active in 2007. According to Angela Petrelli, after a certain amount of regeneration, the person stops physically aging (Cautionary Tales). Also, all the cells in his body are dying then healing, effectively making him immortal.
The burns Adam received from a lightning bolt at the end of Out of Time healed much faster than any other example of rapid cell regeneration in the series, indicating that Adam's regenerative ability may have improved over time. Adam's incredible resilience is also demonstrated in Revolutionary War, Part 2, where he appears unphased despite being stabbed repeatedly in the chest and heart by multiple opponents.
In Four Months Ago..., Adam reveals that introducing his blood into a wounded person's body will cause rapid healing of the injuries.