Well, first, there’s the whole reason St. Augustine speculated the existence of Limbo.
It’s like the question, “Can a person be a good person and not a Christian?” C. S. Lewis answered that question by pointing out, firstly, that a Christian’s definition of a “good person” is going to be different, anway.
So, I think it’s pretty hard to find someone who’s not Catholic who’s “perfectly virtuous” in all respects (barring religion).
Speaking of C. S. Lewis, as noted above, this is the kind of thing where individual conscience comes in: where ignorance, invincible ignorance or insurmountable prejudice may overwhelm the person’s culpability for rejecting the Church.
And, hey, we admire people like Aristotle and Plato.