Are these sentences right?
1. My parents are growing old. -- Yes, correct, natural, idiomatic.
2. The environment in China is growing worse. -- Yes, correct, natural, idiomatic.
3. People grow weaker because of age. --Yes. The use of "grow" is correct. It would sound more natural to say "People grow weaker WITH age."
4. The house prices are growing higher and higher. -- Doesn't sound right to me. It's grammatical, it's understandable, but I would not use "growing." I would use the word "climbing." And "The house prices" isn't right here. These would be correct:
House prices are climbing higher and higher. -- OK
Housing prices are climbing higher and higher. -- Better, more formal
The prices of houses are climbing higher and higher. -- Here's where you could use "The."
Prices of house are climbing higher and higher. -- But this is OK, too.