I think the NASA membership is around 40-45 year...mines coming up for renewal...there are 6 events per year. Typically 3 at motorsport ranch, 1 Texas World Speedway, 1 No Problem, and 1 Hallett.
For HPDE, just show up with a safe car...lots of track time!
The next event is No problem, then TWS I think...
http://www.nasatx.com