I was watching a video from Aurelien Barrau about relativity and time. As he was talking to the audience, he said that since he was walking on stage, he was ageing slower than people sitting in the audience.
I have read that time slows down if you move faster but... in what referential? Maybe I'm faster than you in some referential but not in another! This makes sense if we are talking about light (whose speed is the same in any referential) but what about anything slower than light?