If you travel at the speed of light away from earth for 30 years and back for 30 years, you would arrive back being 60 years older but earth would have aged 4,500,000 years. Something like that.
There are other interesting theories that say that time is not linear. All time could be happening at once. You could die today and come back as a child in 1600.
There are also anti matter theories that state that when you make a decision between various choices, that on another plane, you are making all the other choices as well.
For some reason I love this stuff.... time may just be a human construct to make us feel some comfort but really it's far more complicated than our limited senses can comprehend.