This is a good hypothesis in that you have stated what you expected the results to be. There will be a direct correlation between age and the position someone sits in the carriage of a train. You have further stated that the correlation will be positive meaning that as the age increases the closeness they sit to the door will also increase.
To organize this you will want to define what the independent variable (IV) is that varies between groups being tested to see if there is a difference. This will most likely be the age of the subjects as the age is the focus. The dependent variable (DV) is what you measure change in the IV. Remember that the DV is the same in all groups being tested.