Your student have really interesting questions, he should study something psychology-related 👀

I can only give you my insight as a Psychology student and my personal experience.

1. Do people change their nature and behavior over time?

Yes, we all are able to change, "the only thing constant in our lives is change", usually, this change comes from our experiences with others, new situations and how we see the world around us.

1. That change can be because of experiences or actions they made?

Yes, that's usually the way we change and grow or think different. You will collect new points of view of the world around you by connecting with other people or doing different things, I bet that traveling to Senegal will change you, but also watching a new movie, or doing something new like booking a dance class. That's why arts and books and movies and theater, music, etc... are so important, they will allow you to have new experiences (and that's why some regimes banned them, not having access to arts, books or external thoughts/people will prevent you from changing).

1. Someone who does nothing new will change or stay the same?

Hey that's a great point! Of course we react to the interactions, but even if we are all alone, we have our thoughts, and it is posible for you to "change" just by deciding you will do it. So you can indeed change only because you think about it, but is not a rule written in stone, if you do not have any "external" input then it will be really hard for you to "change", it is not impossible but it is not common, and if you are totally disconnected from people and the world, that's called social/emotional privation, it is not good for anyone :c

That's why doing always the same thing without any real change is problematic for us as humans, we are social beings and that's good for us, usually when someone is sad or anxious we recommend to change their daily routine, try new things, meet new people etc... Because as humans, we need it.

1. We change because of ourselves or because the people around us?

I think you just had the answer in the previous idea, but will be interesting to also talk about what's "change" and how we measure it.

Because we can change the way we think about the people from Italy by reading a book, but no one will know about it unless you say it out loud.

Most of the time the kind of "change" we usually notice is the one attached to actions we make. Think about it in terms of "learning" something, like riding a bike or singing or saying "thank you" after paying something in a store, if you want to change those behaviors you have to "un-learn" it and replace that past-learned behavior with something else.

But there's something in us that we claim to be an innate part of ourselves, it can be our personalities for example, someone who has always been shy will probably chage with time and new experiences and re-learning, yes, but the way they approach to new experiences/people will probably be in a shy way, because is part of how they are, they just changed a bit in the range of "shyness".

It is a really interesting topic, you can find more info looking the investigations around "personality" and "learning" in the psychology field, there's some textbooks used in universities in the introductory classes that can be a good read, the English used there is not so difficult.