People have grown a lot taller since ye olde days of pirates, I'm by no means any sort of voice on this but from what I've read/heard, people are genetically developing to grow taller and live longer. By 2400 it's predicted that the predeterminded lifespan will be roughly 130 years I think, no links as this is from memory.
Split from a discussion over whether 5'6" Edward Teach was a "giant" for his time or not, in the badass figures thread - JB