They are very well written. When it comes to someone’s height, I would usually say “she is taller (shorter) than average/ she is taller than the kids in her age. “

This is very clear and well written. I certainly don't think your English is below average. It's much better than my Japanese! It makes perfect sense to say 'human in Japan' but 'Japanese person' sounds more natural. We don't use the word human that often and mostly in scientific contexts. On the second point, your wording also made sense but the new structure flows more naturally because the verb (is) and the subject (mean temperature) are closer together. This makes it easier to quickly understand. For 'English language skills' you could also say 'English speaking' 'level of English' or just 'English' Keep up the good work!