Bad wolf is right (except that nothing, apart from light can travel at light speed). The friend travelling for 10 earth years at, say, 99% of light speed would hardly age at all, and a trip to the nearest star at that speed would pass quite quickly. The time taken can be calculated using Anders Anderson’s chart a few pages ago.
It is all rather irrelevant though. The energy to accelerate a person to 99% of light speed is enormous. The formula is E(k) = 1/2 m v^2. Basically, to accelerate 1kg to that speed you need 0.5 x 1 x 9 x 10^18 = 4.5 x 10^18 Joules, which is the equivalent energy of about 71,000 Hiroshima bombs. (My calc, based on Wikipedia saying that bomb released 6.3 x 10^13 Joules.) So to accelerate a 100kg human inside (say) a 900kg spaceship to 99% of the speed of light, you need the energy equivalent of around 71 million Hiroshima bombs. That is a heck of a lot of rocket power.