Hi Jess,
Usually, you have to be 18 to work on the railway however there are some exceptions to that - local to you, depending on what area of the business you’re interesting in, ScotRail offer an engineering or a customer service apprenticeship which you can apply for between the ages of 16-25 (unless it’s changed since I last looked but definitely look into it). I started on the railway aged 17 with South West Trains in a part time gateline position then progressed up to becoming a Guard when I was 18 then I managed to land a driving job 2 and a half years ago when I turned 21; age is just a number, providing you’ve got the skills to do the job you’re applying for and you’re reliable, you stand as much chance as someone a bit older.
Also, I know plenty of folk who work on the railway with an ASD diagnosis who all have different skills which they bring to the job, so don’t let that hold you back!
Definitely contact ScotRail (or whoever you’re applying for) regarding what age you’d be considered for jobs, anything safety critical (train dispatch, guard), you’ve gotta be 18 or over and for driver, it’s 21 (however some companies will commence your training when you’re 20). Best of luck for the future!