let 15 year old's join
age is a legal problem for most sites .. including the live steam model parks ... second point is the transport problems ( some of us wish to help out but just cannot get to the locations )
The tram museum will allow a 15-year-old to start training if they come across as diligent and mature, but they can't actually work as a fully qualified conductor for a few more years. You can't fully qualify till 18.
The bigger issue for most societies now is nothing to do with the age of the volunteer as a worker as such - it's that if you regularly have 'minors' working on your site, the other members they work with have to go and get 'working with children' checks done and the minors can't be left alone with anyone who hasn't done this check.
It's an unfortunate fact that the rail preservation movement has had 'issues' in this area in the past. While it's not been made a hard requirement yet, Transport Heritage NSW has been 'strongly recommending' that any rail society worker who works with the public get a Working With Children check done and that the society maintains a register of the same.
If you have a minor helping in the workshops or assisting with maintenance, this requirement spreads into your maintenance crew.
All this extra futzing around with WWC will discourage some groups from taking on keen minors just avoid the extra paperwork burden.