Median Net worth

What would be the median net worth of Americans age 50 and older?

I have attempted to do some research into this and cannot find a clear answer. I have seen numbers range anywhere from 75K to 1.5M. Furthermore, much of the data seems to be outdated (circa 2005-2010). Could it be there is no accurate way to collect this data?

http://en.wikipedia.org/wiki/Wealth_in_the_United_States

The table in the link I gave doesn’t give a total for all those above 50 - but from what it gives I’d estimate the median net worth for households where the head is above age 50 is around 200K. Mean is around 650K.