I've been knitting for about 4 yrs. But my daughter who's not yet 15 is attempting this. It's not that difficult. There's no increaseing or decreasing or patterns to really memorize. It's a garter stitch bottom (knit every row) and the body of the bag is knit every row in the round (which is stockinette stitch). No purling at all.
The most difficult part (and it's not that difficult) is the i-cord strap. But there are videos at Knittinghelp.com that show you how to do everything this pattern calls for. Picking up stitches, knitting in the round, and i-cord.
ETA: I cannot sew to save my life. In fact, this morning I finally gave in and sewed up the crotch to my favorite sweat pants. I have been wearing holey crotched sweat pants for nearly 6 years :blush: