Hmm, one of the oldest anime I can think of from what I have seen is probably this:
https://www.youtube.com/watch?v=EfhWjoInwb0

Anime Three Musketeers



and

https://www.youtube.com/watch?v=tjuN5Bn-RCo

Gatchaman

I did saw Voltron on Toonami in 1998, but it was not my first anime. I do remember seeing VHS copies of it at Hollywood video and I would be like "Why are these VHS tapes so big compare to the others?".

It's kind of hard to tell honestly.
I wanna say the spanish dub of Dragon Ball Z which was completely uncut, i remember watching that. But at the same time lots os people who are my age have Pokemon as their first anime.

I don't remember specifically but it was either Pokemon, Dragonball z or Sailor Moon.

The first two animes I saw were Neon Genesis Evangelion and Akira when I was around seven years old.

My memory is really fuzzy but it was either Sailor Moon or Dragon Ball Z.

I remember seeing Akira around that same age too. Both Vampire Hunter D and Akira was on late night TV on Sci-Fi back in 1998.