Dd did 3 years of kindy and began first grade after being 7 for 2 months. Last year it was hard to see her "stay back" she is very tall and very verbal and her non-Waldorf friends are a grade ahead of her. But now she has friends in the two grades above her and is comfortable socializing with friends who are not in her class.
I saw the wisdom of "waiting" last year when she really gained a deep seated desire to learn and was very motivated. I also trusted her kindy teacher's assessment. She has begun first grade eager and excited. There is another girl in her class who would be in 3rd grade at public school - we also saw her blossom and come into her own last year. She would have been lost if age alone were the criteria for first grade readiness.
The "being held back" phrase is not helpful. It is a gift to your child to let them have a childhood and develop at their own pace, not yours. Your child's age when entering first grade is not a reflection on your parenting
So my dd will turn 18 the summer before her senior year. This is not a bad thing. I taught high school and I saw the huge maturity difference in the 17 year old seniors vs. the 18 year old seniors.
And really, now that Im facing 40, Id rather have one more year of kindergarten than one extra year of working