Disagree. I'm also 5'3 and all of my mountain bikes are normal unisex versions. It has more to do with your inseam to torso length ratio than height. I just ride XS and S mountain bikes.

That bike I linked to will *probably* be too big for you.

Disagree there too. Commonly held myth, but most modern studies are saying that runners are less likely to suffer from arthritis later in life. So why do you hear about some runners having joint issues? Poorly fitting shoes. People wear shoes that don't have the right amount of support and cushioning for their level of pronation, which causes excess torque on the hips, knees, and ankles. Going to a specialty running store can lessen the chances of this happening, but I've seen running stores put people in bad shoes too. It's the same as running your saddle too low and sitting and spinning at 90 rpm for yours...bad fit, and your joints turn on you.