strictly speaking, anything with mass CANNOT travel at the speed of light. but you can get close.
your scenario is flawed btw. a person traveling at the speed of light to a star one light year away and back would NOT see a planet aged 200 years.
the planet would be aged exactly 2 years. however the person doing the traveling would not experience two years of travel he or she would experience less time depending how fast they were traveling, if extremely close to the speed of light that person may have experienced only 1 sec of travel time.
this is because the universe has a speed limited and time and velocity is related so the faster you travel the less time you would experience compared to the rest of the universe.
so if i travel at close to the speed of light for 100 light years out then 100 light years back, the planet may be aged 200 years, but i would feel as though ive only traveled for 2 years.
nothing with mass can move at the speed of light, it would take more energy than available in the entire universe. but suppose that we can, if you do a smooth acceleration there no reason why something would simply disintegrate, unless that is, it hits something. which since it take more energy than available in the universe to accelerate it to the speed of light, it would be a mighty big explosion if it hits something(big bang sized one), anything, a neutron even.