It takes a LOT of energy to get something anywhere close to C. I can’t remember the exact numbers but I recall it would take 99 kg of antimatter to accelerate 1kg of matter up to 0.5 C and then stop it again. Nearly every sci-fi novel vastly underestimates the mundane logistics of interstellar travel. It may turn out to be feasible but not economically viable for anything but long term hibernation ships.
Wear and tear.
Conversely, if you accelerate at 1/2 G, you’ll be younger when you arrive. 
If you pass the speed of light, you arrive before you left, which makes you temporally younger as well.