[ACW]

I have a question for you guys.

So, I was with my friends from Japan and a person they were acquanted with came by to ask help for some homework. When they started talking to their friend they spoke in a different form of Japanese other than speaking informal. After the person left I found out that he was older than them. I also see that sometimes in Japanese television.

So here's my question. When in Japan, is it required to talk to others older than your current age in a formal dialect? Is it to show respect?