How long did he study that sun?

Luke and Linda are star crossed lovers since birth, but alas, Luke was sent to study the sun, and Linda is left alone. Luke travels to the sun to study it for ½ a year and then can return home to Earth for 6 years before he must leave again. Originally, it takes 16 years for Luke to reach the sun because he had a bad rocket, but each time he returns, he acquires a new rocket that is 3/2 times as fast. If Luke first left when he was 18, and died at 136, then how many years was he away from Linda? Round to the nearest whole year.