Ha, just imagine how many extra steps you're taking with those petite little legs!!! I'd say height has a lot to do with it for you.
I'm around 5'4" and yesterday on the treadmill I walked 2.2 miles in 45 min. That was at a speed averaging about 3mph. I just don't know how you ladies can do 3.7!!!! Anything over 3.5 and I feel like I'd have to run to go any faster. I just started about 6 weeks ago, so that's an IMPROVEMENT for me
. I was sweating my butt off, btw!
Guess I agree with the others, we'll get faster as we keep at it. But "just doing it" is the main thing, at least for me right now!!