I don't think that's quite right. Snapchat does have a chat feature which allows you to essentially send feedback on peoples snaps/stories, so you could absolutely tell people they're wrong for making some statement.
It also depends on whether you have friends that use Snapchat. I'm 24 and a college senior, so within the right age group, but none of my friends use Snapchat. It's only fun if you have friends who use it.
But do you think their actual sources of revenue (all the ads and paid stories) are focused towards older people? From what I've seen, it's mostly gossip and stories aimed towards younger people.
Oy, that. Honestly, with all their algos I'm confused why Facebook lets one friend cover my entire feed in Shah Rukh Khan. I don't even know who SRK is!
It's not like Snapchat is an esoteric thing. Using it can be a function of how outgoing and expressive you are. Or if you have some purpose.
The same reason you post on Hacker News is why people post on Snapchat -- to interact with others.