I was curious and searched Duck Duck Go (which I now use in preference to Google) for "average female weight", and was surprised to be immediately presented with "Answer: 144 pounds." I was used to using Duck Duck Go for simple mathematical calculations (same as Google offers), but didn't realize Wolfram Alpha included that kind of information. In any case, this answer was obviously incomplete, and I was interested in historical trends; even aside from the frequent news reports about our growing girth, just by pure non-scientific observation I felt that a woman my size - currently 5' 4", 118 pounds - would not have been described as "skinny" when I was born 42 years ago.
I found an article containing data from a CDC report on height and weight trends from 1960-2002, and downloaded the report itself. Apparently, even in 1960 the average weight for an adult American woman aged 40-49 was 142 pounds. As of 2002, it was 168 pounds. These are mean averages, and the standard error is listed in each result table, so those with more scientific background than I have can analyze and judge the results for yourselves.
So, maybe I am skinny? Does it really matter? Being fit matters to me, certainly. But things related to fitness that are more important and relevant to me than appearance or the number on the scale are:
1. Avoiding medications. I absolutely hated taking daily meds for depression (the only one of which that was helping landed me in the ER with a grand mal seizure), and would hate to be dependent on them for combating high cholesterol, blood pressure, or diabetes.
2. Physical readiness. Being able to walk a mile uphill rather than wait 15 minutes for the next bus, for example, is wonderful. So is the ability to be physically active for most of a 4-5 hour shift at the Free Farm and Free Farm Stand.
3. Stamina. Still working on this one, as I do tend to tire mid-day. But I generally have more energy than I did when I was heavier.
So, sure, add skinny alongside vegan, atheist, bisexual, polyamorous, and all my other freak flags. Fitting into the mainstream has never been a priority for me anyway.