Hi MK! That's a beautiful sheath and you have a killer figure, but I think I have to agree with the others that it's a tad too short for the office. I think zippered sheaths are really big right now, and if you hold out you may be able to find one that you would feel more comfortable in length-wise. I'm keeping my fingers crossed for you that the misses size works!
I don't think it is too young. I'm also in my fifties and I have had good luck with Calvin Klein. Here is one, similar to the Michael Kors one, that I ended up keeping:
http://i658.photobucket.com/al.....h003-1.jpg
And here is another CK sheath with an exposed zipper that I returned because it was a little too snug for my bootie:
http://i658.photobucket.com/al.....kdress.jpg
For office wear, here are a few examples of ones that look like they might hit right around the knee:
http://www.bluefly.com/Marc-Ne....._553894776
http://www.myshape.com/shop/st.....ductSearch
http://www.calvinklein.com/pro.....d=10801368 (I love this one, but one zipper dress is enough for me!)
I love the ways you styled the dress, btw. You have wonderful style!