Questions about example sentences with, and the definition and usage of "Restrospect"

A: × In restrospect, when he was in his early teens，he was so shy that he couldn't even make friends easily .
✓ when he was in his early teens，he was shy so he couldn't make friends easily .

× However, he was inquisitive and exceptional in languages and being baptized.
✓ However, he was inquisitive and had exceptional language skills.

× That is why later on, he could dedicate himself to helping inaccessibly situated poor and sick Asian people free of charge.
✓ That is why later on, he could dedicate himself to helping poor and sick Asian people free of charge.

× Each one of us should learn his courage and spirits and make the whole society more wonderful and colorful.
✓ Each one of us should learn from his courage and spirits and make the whole society more wonderful and colorful.

I don't understand "and being baptized". Maybe you meant "he was baptized" or "he baptized others"?

"In retrospect" should be followed with something you should've realized. Something like "In retrospect, I should've realized that..." or "In retrospect, ...should've told me that"

Phrases like "he was so shy that ..." should be followed with an example:
- "He was so shy that he didn't have a single friend"
- "He was so fast that he raced boys two years older and won"
- "He was so fat that he couldn't fit in one seat on the train"

"Exceptional in languages" doesn't make sense, you need to say something about his skills with languages like "exceptionally talented with languages" or "had exceptional language skills".

"learn his courage and spirits" means "memorize his courage and spirits". "learn from" is the phrase you use in these situations.