How do you/would you/have you recruited a co-founder or mentor

Recruited, for lack of a better word.

I know a lot of people meet up in college - I haven't been so lucky up until this point. In the past I haven't met anyone qualified enough to be a real co-founder or mentor until recently. I've put a lot of effort into all of my projects and am set to start a company, and I'm sure choosing the right people is extremely important. As such, having already started on my own, I'm wary to let someone who hasn't yet contributed in on all of my work.

What's a reasonable way to proceed? Should I just bring them on and offer them the farm? Should I toss them a heap of legal work?

Does age play a role? Should I look for an older, experienced co-founder/mentor or a someone young with time on their hands?

How do you decide how shares are divided?

I recognize these questions don't have a precise answer, but I'm looking to get a broad perspective of how it's been done before.