I am single, almost 62 and I hate my location here in central CA, but all 4 kids & grandkids are here and I probably couldn’t uproot them. So I’m stuck. You may be in a similar situation, but 4hrs away ain’t all that bad.
Just a suggestion: I fell in love with Kanab, UT during my recent vacation. Depending on where you call home in Central CA, it might be an 8-10 hour drive, but your grandkids would love to spend summers with you, due to all of the National Parks in the area.
OTOH, my grandson lives about 30 minutes from us, and I can't imagine what it would be like being farther away from him.