1. He is past old age, so he is very weak. He is about to pass away.

2. He is past middle age, so he has to work hard to prepare for old age.

3. He is past young age, so he is able to cope with difficult tasks.
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Are they all grammatical? Would yoiu check them? Thank you.

#s 1 and 2 are fine.

#3 is phrased strangely. Try this:

He is not in his 20s anymore, so he should be able to handle difficult tasks.

Yes, I can help you check the grammar of these sentences. Here is the analysis:

1. "He is past old age, so he is very weak. He is about to pass away."

This sentence is grammatically correct. It describes someone who has reached an age beyond old age and is consequently very weak. The phrase "about to pass away" suggests that the person is near death.

2. "He is past middle age, so he has to work hard to prepare for old age."

This sentence is also grammatically correct. It states that someone has exceeded the stage of middle age and, as a result, must exert effort in order to get ready for old age. The use of "prepare for old age" implies that the person wants to ensure they are well-equipped physically, mentally, or financially for the challenges that come with old age.

3. "He is past young age, so he is able to cope with difficult tasks."

This sentence is grammatically correct too. It indicates that someone has surpassed the period of young age, implying they are no longer young. The phrase "cope with difficult tasks" means that the person can handle or manage challenging responsibilities or assignments effectively.

Overall, all three sentences are grammatically accurate in terms of sentence structure and word usage.