Considering employment hours below 18 I would suspect not, as only being allowed to work 4.5 hour stints before a break would not be efficient use of a time for a TOC, compared to employing somebody 18+.
That's the same for everyone, not just under 18s.
The biggest restriction for those under 18s is that they can not work between 10pm and 6am (11pm and 7am for railway related work).
Another thing for those under 18, they can't have any safety critical jobs, or work on board trains, so if you do apply to a TOC for a job, be prepared to be a general dogsbody and/or cleaner on a station.
If you want to get a customer focused job on the railways and seeing your only 16, then I recommend you volunteer at a local charity shop (British Heart Foundation (Furniture and Electrical) for example). This will give you a good entry on your CV (providing you volunteer long enough), plus get you a reference that's not from college/school.