Hi,
I'm 40, 5'9" barefoot, and about 152 pounds at the moment.
My elbow bone spacing is about 2.7", so I've got a small frame according to [link|http://www.aomc.org/HOD2/general/weight-HEIGHT_W.html|this] page, meaning I should weigh 144-154 (in shoes). I think I feel best around 140 but haven't been there for several years. I'd be happy to consistently be below 145.
I was closer to having Scott's metabolism in college when I exercised most every day and did lots of walking (but didn't also have a full-time job like Thane). I was around 125 pounds then.
Gotta get back in the exercise routine to lose 10 pounds around my gut...
Cheers,
Scott.