The statement about 1965 is not correct if you take into account dividends. The longest periods of being down (in real terms) is 1973-1985, 2000-2013, 1937-1945, 1916-1925
( https://observablehq.com/@tcgarvin/shiller-sp500 )
I graduated from high school in 2000, and sold my first company to Google in 2011, insisting on cash and not stock given the performance of the market through my entire adult life ;)
Thank you for the correction. I had mistakenly thought that the chart was total returns rather than just index price, but looking closer I think you are right.