Does the sentence People are living longer mean people will live longer or people have tendency to live longer? Does the usage of the present continuous tense in people are living longer and children are leaving home result in the same meaning?
- These days, people are living longer.
Here, we want to say that according to statistics, people have been dying at a more advanced age in the recent period compared to a period preceding it. Hence, the people who are alive at the moment have more chances to live a longer life. To say in simpler words, you are right: it means "people have a tendency to live longer."
- These days, children are leaving home less often than in the past.
In this context, what we want to say is that children are less likely to go away from their home nowadays. This sense is parallel indeed to "people are living longer" of sentence 1.
- Our children are leaving home tomorrow morning, they will study abroad for 5 years.
In this context, we speak of a specific event that is planned to happen in the near future. This sense is not parallel to "are living longer" of sentence 1.
Could you use the phrase "to live longer", which is used in sentence 1, in a fashion similar to the fashion used in sentence 3? In most contexts, no. "Living longer" is not usually an event you can plan in advance with certainty, like travelling on a train.
We can try:
- A group of convicts awaits execution. Suddenly, a messenger arrives.
He dismounts from his horse and walks up to the executioner. He wispers in his ear.
" - By the word of the King, these two people are living longer."
" - What?"
" - "You will halt the execution for these two at the last moment, and I will announce that their death penalty has been exchanged with 20 years of hard labour."
Here, I used the pronoun these and the numeral two to make the whole thing more specific. And the words "are living longer" refer to the planned last-minute reprieve, a specific event in the near future.
People are living longer would usually be taken to mean that on average, people today are living longer than they did at some unspecified time in the past.
Children is leaving home is grammatically incorrect, it should be children are leaving home. This one does not have such an obvious meaning without a bit more context, but it is the same tense in general and is very much the same if you use it in the context of a societal change (a meaning like fewer adult children are living with their parents today than in the past.)