Is it safe to drink diet pepsi from a can that is over 4 years old?

No, I don't think its that safe because its been so long and you might be ill if you do drink it

But if you do have a diet Pepsi can in your house for over 4 years and you want to drink it then you should probably look out for these and if it is one or all of these things you should not drink it at all:

1. It smells gross or different than it should smells like

2. The colour has changed so for example it has changed from black to grey or green

3. There's fungus all over it! It can be outside the can or inside I'm not so sure

That's it if it doesn't have any of those things then I guess its safe to drink

But remember you should really ask your parents before you drink it, but I seriously wouldn't!