It's possible and everyone will understand what you mean " to MAKE SOMETHING ADULT" but it is not commonly used at all. +ify means "to make something...x".

Ugh. I don't like it. My reaction is "that's not a word, and if it is, it shouldn't be." As Ruthi says "everyone will understand it." In English it's fairly common to coin words by combining prefixes or suffixes that may not have been used before. Unfortunately, I can't think of any "real word" that means the same thing. I think it's OK to use it in ordinary, everyday speech, even in a business meeting, but personally I wouldn't. But I can't imagine a situation where I would need to. If you are making a formal speech to a group, or if you are writing, I would check a dictionary and I would not use it until it had been accepted in a standard dictionary. Certainly in a half-joking context, I could say to friends any of a number of things, invented on the spot, like "let's add some hot sauce to tastify this food" or "I bought more RAM to speedify my computer,"