"The former" would be better.
Although "the old" is correct, it means it is not new or modern.
To be honest, we use "old" quite a bit more than we use "former" in informal speech. Most native speakers have no difficulty determining the meaning of "old" based on the context. For instance:
"I ran into my old boyfriend at Barnes and Noble, yesterday."
We know you mean your ex-boyfriend and not your 90 year old boyfriend.