Yu could get a saturday job in a hairdresers to see if you liked it, if you did they might offer to pay for your training
You would need a qualification to work as a Travel agent , but again could go in as a junior role and get them to pay for your training.
A holiday rep you wouold just need to apply for it and go and try it out, but it is very hard work. Having spoken to reps abroad they usually work a 12 hour day, with extra's on top of that, like attending excursions and night events also going to the airport at night. One of the girls I met said you were also expected to go on the excursions on your day off to get the guests perspective. They do have a good social life, partying between midnight and 8 in the morning!!!