There's nothing to prevent them from actually learning before age 5. We exposed my daughter to reading, and she learned to love reading before she started school. She remained several years ahead of her age group all the way through university.
All without the benefit of "Head Start," or any other government indoctrination program.
I still remember my big brother teaching me the alphabet, etc.
We were raised by my grandparents on a little farm in the north woods.
When I went off to school - the little one room, one teacher school - “Sub primary - 8th) I was so proud. I knew my ABC's and could write my name.
When we left and moved to the big city - Boston - we were a full year ahead.
He went on to become a specialist in radar, sonic and space engineering, responsible for space stations on the east/west coast and the Altlantic and Pacicifc.