<human>: Can you provide a brief rundown of the text in within 3 sentences?

So I've taken up running recently, it's pretty enjoyable, and I was seeing  a drastic increase in endurance right off the bat. I thought building endurance would be the hard part.

 Instead, I'm finding myself running up against a wall (no pun intended), not because I get exhausted or out of breath, but because my knees start to hurt terribly long before I even work up a good heart rate. 

 I'm 21, 180~ pounds, no pre-existing injuries or conditions that I know of. I don't think I specifically injured myself, as I assume one knee would hurt, not both. I've only been running for a couple weeks now, about a mile a day, I'd be doing more by not if not for the knee-strain.

 Basically: Is this normal for someone new to running, who spent a few years mostly sitting around idle? Am I just feeling a bit of ache building up unmaintained muscle, or injuring myself? 

 I havn't had a bit of soreness anywhere else.
<bot>: My knees are holding me back. Should I destroy them and replace them with bionic parts or just keep dealing with them until they carry me properly?