Hi Min, I also dont think you should stress too much about it!
Aidyn didn't start crawling until he was 10 months as well... he never commando crawled, just started crawling on his hands and knees at 10 months.
And it didnt take him much longer to start walking after that - he took his first step at 12 months, and was walking properly by 13 months!

I know how hard it is when other people's babies do things before yours... I have had many worries about that in the past, and still do!
But try not to let it concern you too much, as I'm sure he is just taking things at his own pace which is perfectly natural and normal for him!