Check out their website. They have an application process and required training. Age is not mentioned, but it worth a call to their office in ABQ to find out if there is a minimum. If a parent or guardian works/participates with you an age barrier may be overcome.
There are quite a few railroad organiations that are youth friendly when a parent participates. There can be restrictions (federal) to non-adults participating in dangerous activities like cooking french fries at McDonalds.
It's worth the effort to find a way to make volunteering work as you will learn a lot. Young people can have tremendous credibility with people their age and younger serving as docents. You will also learn how to work with adults. It's a win win deal.