Reported Speech

No.

So would the age have to be expressed in the present tense? What if you didn't know them? And you want to talk about them to your friend. Would you have to use the past tense otherwise?

It would make more sense to give their age in the present unless the befriending was a long time ago. If you don't know them, then you probably don't know their age, do you?

That's true but what if you saw them downtown, didn't necessarily know them but want to talk about them by approximating how old they are, would that change the way the tense is given?

I saw four guys downtown today and they were about 25 years old.

Yes, I agree with gravedigger, zapeti. I would definitely use past tense then. The men are definitely a past experience.

Alright, thanks.

And another thing, If I want to talk about a group of people that I met long ago, and I didn't know them, do I say "I met them once but I didn't really know them" or "I met them once but I don't really know them"

It depends on whether they are around now.

What if you're not sure whether they're still around?

Then you'll just have to wing it.