It would be the ideal life for (me in) my old age. It would be the ideal life for (me in) my old age.

The most exciting thing [during my trip / during this timerip] was swimming in the sea. The most exciting thing [during my trip / during this trip] was swimming in the sea.

Note: there’s nothing wrong with what you wrote, grammatically, but we wouldn’t say “during my trip this time.” For 我这次的旅游 we’d say “during my trip,” “during this trip” or “the most exciting part of this trip was….”

I first swam when I first arrived there and then I swam the next morning. I swam when I first arrived there and then the next morning.

"first" goes with "arrived" so is near it in sentence. You don't need the second "I swam" as you have it earlier in the sentence.

I first swam when I arrived there, and then I swam the next morning. I first swam when I arrived there, and then I swam the next morning.

This is a little picky, but a comma should be in there!

The feeling that when you are at a beach, seeing the endxpanse of the sea, blowing against the sea windfeeling the sea breeze in my face and body and swimming in the sea is very nice. The feeling when you are at a beach, seeing the expanse of the sea, feeling the sea breeze in my face and body and swimming in the sea is very nice.

I’ve edited my corrections based on your comments.

The feeling thatof when you are at a beach, seeing the end of the sea, blowing against the sea wind and swimming in the sea is very nice. The feeling of when you are at a beach, seeing the end of the sea, blowing against the sea wind and swimming in the sea is very nice.

The feeling that when you are at a beach, seeing the ewind of the sea, blowing against the sea wind's edge and swimming in the sea is very nice. The feeling that when you are at a beach seeing the wind blowing against the sea's edge and swimming in the sea is very nice.

Where water meets land it is an "edge" not an "end" e.g. sea's edge, lake edge etc.. It's possible I am misinterpreting what you are trying to say here "seeing the end of the sea, blowing against the sea wind"?

Theat feeling that when you are at athe beach, see looking at the end of the sea, blowing against theless sea, feeling the blowing sea wind, and swimming in the sea is very nice. That feeling when you are at the beach looking at the endless sea, feeling the blowing sea wind, and swimming in the sea is very nice.

So I suddenly had an idea to find a medium-sized coastal city where I could see the sea, blow againstfeel the sea wind/breeze and swim in the sea all year round. So I suddenly had an idea to find a medium-sized coastal city where I could see the sea, feel the sea wind/breeze and swim in the sea all year round.

So I suddenly had an idea to find a medium coastal city where I could see the sea, blow against the sea wind and swim in the sea all year round. So I suddenly had an idea to find a medium coastal city where I could see the sea, blow against the sea wind and swim in the sea all year round.

I'm not sure what you mean by "blow against the sea wind" but I've never heard that statement. I'm not sure how to correct it because I'm not quite sure what you mean.

So I suddenly had anthe idea to find a medium-sized coastal city where I could see the sea, blow againstthe wind blowing on the sea wind's edge and swim in the sea all year round. So I suddenly had the idea to find a medium-sized coastal city where I could see the sea, the wind blowing on the sea's edge and swim in the sea all year round.

medium-sized rather than medium to describe how big a city is in this instance.

So I suddenly had anthe idea to find a medium-sized coastal city where I could see the sea, blow againstfeel the sea wind, and swim in the sea all year round. I suddenly had the idea to find a medium-sized coastal city where I could see the sea, feel the wind, and swim in the sea all year.

This kind of place can only be found in the southern part of China, like Guangdong, Guangxi and Hainan provinces, because coastal cities in the north of China are very cold during the winter. This kind of place can only be found in the southern part of China, like Guangdong, Guangxi and Hainan provinces, because coastal cities in the north of China are very cold during the winter.

"southern" is the adjective.

But tThe houses in coastal cities are all expensive. The houses in coastal cities are all expensive.

When speaking out loud, it's okay to start a sentence with "but" but in written language, it's "improper" to start with "But".

But theHowever, houses in coastal cities are all expensive. However, houses in coastal cities are all expensive.

I hope I can find a small one that is not thatoo expensive. I hope I can find a small one that is not too expensive.

"not too expensive" for a house that you can afford to buy / rent.

After I buy a house in a coastal city, I wouldill spend my time on a beach, swimming, bloweing againstcaressed by the sea windbreeze and [seeing the end of the sea | gazing at the horizon]. After I buy a house in a coastal city, I will spend my time on a beach, swimming, being caressed by the sea breeze and [seeing the end of the sea | gazing at the horizon].

After I buy a house in a coastal city, I would spend my time on a beach, swimming, blowing against the sea wind and seeing the end of the sea. After I buy a house in a coastal city, I would spend my time on a beach, swimming, blowing against the sea wind and seeing the end of the sea.

Again, I'm not sure what you mean by "blowing against the sea wind"

After I buy a house in a coastal city, I would spend my time on a beach, swimming, blowing againstwatching the sea wind and seeblow and watching the end of the seawater's edge. After I buy a house in a coastal city, I would spend my time on a beach, swimming, watching the wind blow and watching the water's edge.

After I buyIf I bought a house in a coastal city, I would spend my time on athe beach, swimming, blowing against the sea wind and seeing the end of and feeling the sea wind and looking at the sea. If I bought a house in a coastal city, I would spend my time on the beach swimming and feeling the sea wind and looking at the sea.