I have a two year old boy with a June birthday. I'll almost definitely hold him back from K, unless he turns out to be extremely mature or a genius

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Whens the best time to "repeat"? He's in a two's program in preschool now. Should he repeat the two's, repeat Pre-K, or do a Transitional K?
Repearting the two's in some ways sounds ideal because he'll have no clue, whereas by 4/5 years old he will be aware that his peers are moving ahead. However, repeating the two's means I'm kind of committed to redshirting him.
Thoughts?