No matter what you do you need to know the age cut-off for entering Kindergarten for the school he will be attending.
So will your son be turning 7 in Kindergarten, if you hold him back?
In my State per public school, kids enter Kinder per a cut-off date. Kindergarten is for kids who will be or are, 5. Thus, some kids enter at 4 then turn 5. Or enter at 5 then turn 6, while in Kindergarten.
IF a child is say 6 already and will turn 7.... then that child is entered into 1st grade. UNLESS, the parent requests that their child enter into Kinder at that age.
Being the "oldest" in class... is not always something that all kids like.
It is a generalization.
I work at my kids' school and see kids in all grades through 5th grade, that were retained or entered into Elementary at a later age.
It does not automatically make a kid better or more adapted or more mature.
Academic ability and social maturity, is also 2 different things.
As far as this year, quite bluntly... I see NO difference at all... in the kids that were retained, or entered into Kinder at an older age per maturity or academics.
They are not necessarily more mature or socially better, just because they are "older." And not always academically, better.
Also, if a kid is older and is the oldest... in the later grades say from 4th grade... they will be hitting puberty and bodily changes, ahead, of their classmates. So think about that aspect too.
I know of a couple of 5th graders, that were retained, and well, they are or will be 12. Meanwhile, the rest of their grade level, is either 10 or will be 11 years old. And these boys are "older" and bigger and it is visually, apparent. And they are not more mature nor academically better or more "confident" just because they were retained. And YES they know they are the OLDEST in their 5th grade, and so do all of the other classmates. One of the boys is already getting "pimples" on his face.
Any kid/person, has a personality.
If a kid is tenderhearted, having them enter school older/later, will not make that go away.
Your son seems socially fine.
But you say he is "fragile."
Well, I see lots of kids, from Kinder to 5th grade, that are that way. They are just, perhaps sensitive or more feeling oriented.
Fine. But a kid also learns resilience and about adapting. And with a parents guidance, they also learn about life's situations and how to manage their reactions/speaking up/knowing their own cues and following their instincts.
It is not only age related or per "when" a kid enters school. It is also how a child's personality along WITH the parent's guidance... learns how to adapt. Gain resilience etc.
It is multifaceted.
Not just about age.
I have 2 kids, a boy and girl. Both are late born.
They both entered into Kindergarten in the Fall- the start of the school year- per school cut-offs, and were 4 years old then turned 5 in Kindergarten, a couple of months after school started.
And they both did fine.
They are both different individuals, and they both did fine. And are fine now, even in their respective grades, both socially and academically.