I have never, ever heard of this expression. Here are a couple of expressions that you might hear in English that involve the adjective 'old,' and words that seem to refer to foods. "What do you think about that, old bean?" The above is an old-fashioned English (as opposed to American or Australian or South African or anything else) way of asking a question of someone with whom you are friendly. It was the sort of thing that posh people would say... and it's just possible that you might hear this phrase, these days, if you watch an old English period drama. "Not this old chestnut again." The above expression refers to an idea that is constantly being mentioned and discussed - the saying suggests that the speaker is sick of hearing about it.

"Old tomato" is not an expression in English. Perhaps if you posted the sentence, I could figure out the meaning. "Rotten tomato" is a common expression for a tomato that's past its prime and "gone bad." It's used figuratively to describe a person who has turned to crime or bad behavior. It's also common to use "good old/ole" or "big old/ole" to describe something. For example, "He's a good ole boy or I drive a big ole car. In these sentences "ole/old" gives the first adjective (good or big) more meaning/emphasis.