pmda wrote:But if you wanted to write it as a perfect passive verb it would be exactly the same....right?
No, because not all adjectives are formed from perfect passive participles (the fourth principal part). Many adjectives are just that, adjectives. Maturus, a, um is an example. If you wanted to make this a compound verb, you'd need to write "maturatum est," which comes from "maturo, maturare, maturavi, maturatus."
Generally, perfect passive participles can be used as adjectives without problem, but the reverse isn't necessarily true.