I echo what has already been said, and I'll offer a little story, free of charge:
My group has the benefit of having numerous (actually, all of them) individuals who are capable, and more importantly, willing, to take on the mantle of DM. But we all had to start somewhere.
For me, it was taking over the reigns while our (at the time) most experienced DM kept a watchful eye over my campaign. It started off as a one-shot, and wound up growing to a 3 year, multi-planar escapade that our group (current and retired members) still talk about.
I had never DM'd before, and had only played for about 6 months, but because I had the support of my friends, it would up being a great experience for everyone. They were a little leary at first, but we all knew and respected what we did, and it led to years (15 years with the same group with only a few changes to the lineup)of great times and memories!