Time was invented to sequence events, to record what happened first, and what after that. Just like a label. We never realized when time took control of our lives. Things went wrong when we thought of time as an absolute entity, shared by everything and everyone. Is time really same for everyone?
As I see, time is not same for everyone. Putting it simply: when speed (w.r.t. clock time) of some action gets slow, it's because of its time getting slow! Assuming time is absolute makes many thing simpler, looking it the other way can explain things which otherwise have no satisfactory answers.
When you are feeling bored lazy, your time goes fast, you spend like an hour while your watch shows that only 15 minutes have passed. Similarly when you are excited, enjoying, your time goes slower. No doubt being happy makes you live longer i.e. with respect to the clock time.
Some people seem to age faster, others look younger just because their time passes at different rate.
Some people can solve problems quickly, because their time passes fast. While you think they solved the problem in seconds they actually took a minute of "their time" to solve it.
Oh, by the way, if you have realized I just discarded "Time Travel" concept as viewed by most of us :).