I think I'm level 23 or 24, I'd have to check :3

There is no cap, someone had made a mining thread about how fast your drill is at a certain level. The fastest it could go was at 99 or 100. There's achievements for levels 1, 10, 30, 50, and 100.

And yea, I know it's slow, but it will get faster. I've been able to make a profit from it, though I use it for only one gun. I sell the rest of my minerals.

(Got to edit more): I've noticed on every level up I get now, the rocks you need to mine is 100 added each time. So it's better to mine now. A while back before they changed this it was more rocks.