THOSE were the days, he thought, struggling to climb up the hill to his house. In his day, he was considered one of the fastest runners in the entire village. In the good old days he could reach the top of the hill in 15 minutes flat.Why, it seemed like just the other day that he had raced his friends to the top of the hill! It was a little late in the day, he knew, for him to aim for the 15-minute ascent, but these days he did spend a good deal of time thinking about his childhood.

He had loved this little village from day one, ever since his father had built a house here. Most of his days as a student had been spent in the village. And to this day his love for the place had not diminished. In those days the hillside was covered with trees. But then day after day, the trees had been cut down to make room for more and more houses. The construction activity seemed to continue all day and night.

He often thought it was surprising that even in this day and age, no one seemed to spare a thought for environment. He knew that the days of tree-lovers like him were numbered and any day now there wouldn’t be even a single tree left in the village. And the day might come when even his beloved village wouldn’t exist any more. I hope I won’t live to see the day, he thought with a shudder.

Those were the days: used to say that a time in the past was better than the present time

In his or her day: during the most successful part of someone’s life

In the good old days: the time in the past that you think was better than the present time

The other day: a few days ago, recently

It’s a little late in the day: used to show disappoint- ment because it is too late for something to be effective

These days: now

From day one: from the beginning of a process, activity, etc

Someone’s days as or with something: a period of time in someone’s life when they were doing a particular job or activity

To this day: even now, after so much time has passed

Those days: used to talk about a situation now, especially if it used to be different

Day after day: happening continuously for a long time

Day and night, night and day: all the time, continuously

In this day and age: used when you are surprised or annoyed that something happens or still happens

The days of something were numbered: used to say that something would soon become rare

Any day now: very soon

The day will/might come (when): used to say that something will definitely happened or might happen at some time in the future

(Live to) see the day: to experience something that you thought would never happen

(Reference: Longman Advanced American Dictionary)