As I was looking up the word ey in dict.cc, I noticed a rather interesting colloquial expression:
What does Aldää mean above? I could not find the word in the Duden or any of the four other online dictionaries I use.
Tofros answer is not wrong, but imho there is a different angle to it.
First of all "Aldää" is phonetic spelling for "Alter". This is German slang. It used to be teenage slang but by now it's pretty much general slang since the teenagers from back then are now 30+ and still use it.
In your example it is used as a form of adress. The translation to "Whazzup?" is kind of incomplete. I would say it's something like "Whazzup dude?". So "Alter" would translate to "dude", "man", "bro" or the like.
"Alter" can also be used as an exclamation. E.g. "Boah Alter!" would be something like "Awwww maaan!".
Literally it also translates to "age" and "old man" but in this context it means something completely different. Most people will not think of the original meaning when they hear it.
In northern Germany there is a similar slang. Often "Digger" is used instead of "Alter". Again "Digger" is phonetic spelling for "Dicker" literally meaning "overweight person" and again this original literal meaning is widely ignored in that context.
The English analogy would be "bro". If I call someone my bro, no one would assume that he is my blood relative.
Indeed Alter is used in colloquial (once teenage) slang to express astonishment, or to address friends. Both of these usages are not too recent really, as similarly used proverbs did long exist:
Today both proverbs are elliptically shortened.
I'm also a native Speaker and would like to shed some light on the usage of all these terms:
As someone from Franconia, I’d also like to add what all other answers have glanced over: Aldää! doesn’t sound like the canonical Alter! to me. It much more closely resembles the colloquial expression for Alte, which I would probably render as Alde or, especially if the end of it is stressed and dragged out, as Aldä(ä) (a match in writing).*
Alde is a bit different in usage.
Some male friends may refer to their girlfriends with this expression when those aren’t present (Mei Alde is‘ im Playboy drin! and Ka Alde, ka G’schrei are samples taken from lyrics by the band J.B.O. (might be considered NSFW))
It’s also used by some – I’d say primarily and by cliché older or even elderly – husbands to refer to their wives and likewise to call and address them, especially in folk comedy shows. (I would expect it to be said like Alde, was gibts’n heud zu Middach? (Ehefrau, was gibt es denn heute zum Mittagessen?).) (I still vaguely remember such a show from when I was a child but I can’t recall its name. Trying to rediscover it (without luck), I at least found some other written samples.)
*: I would describe the sound as something inbetween the two (It doesn’t feel to me like any of the two really covers it, maybe just like the ending -er doesn’t exactly sound like E and R pronounced one after the other.)
Aldää comes from "Alter" (old person, friend), but it does not mean in any sense that the person is old. It is more used between young under-educated men/boys. There is something similar, "mein Alter", "meine Alte", which means "my boy-friend", "my girl-friend" or also husband/wife. This is also used by older under-educated people, and it is not so modern. In former times "mein Alter" meant also "my father", "meine Alten" meant also "my parents". "Wohnst Du noch bei Deinen Alten?" = "Do you live still at your parents?". But I think it is mostly not more used in that sense now.