Green,
Your DS sounds a lot like my DD. (birth month as well as personality).
1st thing 1st. He is doing 1st grade level and keeping him in pre-K is a very BAD idea. Most of pre-K is learning alphabets and numbers but mostly pay time and nap time. He won't find any challenges in school. Believe me, he will find friends. Kids that young do not judge and he will find some friends. If you want to accelerate that, invite the whole class to early Birthday party.
After seeing how he does in Kinder, you can decide whether to put him back in kinder or move to 1st grade in public school. Check the gifted program. They usually test the kid if you request acceleration and you can decide upon the test result.
Most of the time, popular kids are outgoing kids. If he is into sports, being small and young in the grade level makes it harder to compete at the school. Summer leagues are different matter. My DD did not bike on her own until last December (she turned 10 and when her younger sister bike without training wheels). She was scared to ride without training wheel but when she was ready, she asked me to take it out.
Some kids have physical attributes but many of the kids (in this forum) has better intellectucal attributes. We (my family)address their shortcomings and celebrate their achievements. We as parents want our kids to excel in everything they participates in. But the matter of the fact is they may be good at something and not as good as other thing. At least, my 2 DDs are bad in sports. We gave them swimming lessons and tennis lessons (at their requests) but we know that they will never be able to compete successfuly at the tournaments.
I have been in your shoes before. He will be fine and so will you.
