I actively do, at least 1 person (I don't know) each year who's in my career track as well as the people who work for me. The way I get people to mentor is by telling colleagues that if they know anyone who might benefit from talking to me send them over and we'll see if we hit it off. That gets me about 1-2 people a year, some whom still seek me out years later.
I didn't start mentoring anyone until 15 plus years into my career, or so I had thought. After I was first asked to mentor I read up on what it is and realized I'd mentored many people in software since the moment I'd left college. Not all mentoring looks the same but the thing it always has in common is listening, asking questions, listening more then hopefully getting the mentee to listen to themselves. The best book I ever read on mentoring was "Inner Game of Tennis" despite it being intended to teach coaching. I highly recommend it.
I think you can mentor people outside your discipline if you know what questions to ask. It's not always about having a superior technical insight, if it is then it's probably coaching. FWIW I see mentoring as advising someone through personal growth area and coaching as directly training someone on skills improvement or change, the former initiated by the mentee, the later the mentor.
Everyone here is smart and has something to offer. Seek out mentors yourself and in turn mentor others when the chance arises, you'll grow tremendously.
Great question, thanks for asking.