Census age could possibly be 19 rather than 79, which would have made his birth year 1831 rather than 1771. That would be more consistent with the ages of the fellow miners on that census page.
[S490] 1850 United States Federal Census, Ancestry.com, (Name: Ancestry.com Operations, Inc.; Location: Provo, UT, USA; Date: 2009;), Database online. , Butte, California, roll M432_33, page 8, image 18.
Record for W Brasfield