This issue has been covered on ELU, but it's worth noting the first comment to the question in that link - This is a question about an obscure feature of English that makes no sense.
Paraphrasing part of a comment from one of our most knowledgeable contributors on ELU...
think does allow an infinitive complement with Raising to Object, provided it's passivized:
He is thought to be about 50 is grammatical,
I think him to be about 50 isn't passive, so it's "ungrammatical" (according to some "grammarians")
Besides OP's find and my think, several other verbs can accept an "infinitive complement" (X to be Y). But not all verbs work in all cases, and there's no simple rule, and no universal agreement on what is or is not "acceptable". Whereas the equivalent find/think/know/suspect [that] X is Y is always okay.
My advice for learners is simply to ignore this (increasingly, outdated) construction. It should be easy enough to understand the usage, but I don't see much point in trying to produce it yourself. It's never necessary, so why take the risk of getting it wrong?