Besides what danielsangeo said, the part “their worm never dies and the fire is never quenched” is a quote from Isaiah, which is a poetry with lots of metaphors.
Now, could Jesus really have meant that as a metaphor for hell? Well, he might, and he might not.
My conclusion is that there are three possibilities:
- People at that time already knew the concept of hell (which is hard to believe because hell is not mentioned in the Old Testament, maybe it appears in other pre-Christian Jewish books that are not part of the bible and I don’t know about it),
- Jesus presented the concept of hell to the people (which, to me, isn’t reasonable because he doesn’t give a better explanation of what is hell and how it works and people would have requested that kind of information),
- Jesus didn’t say anything about hell.
I just thing option (3) is more reasonable. However, any of the three is possible.