[Dammit. The logic is sound. Now that he's looking closely, he can see the resemblance in the face, even if he's never seen his grandfather without his beard. Jotaro's posture and expression slowly become less hostile, though still guarded.] ...Joseph Joestar does have a Stand. Hermit Purple.

But the age... [Wait. He's got it. He's from the late 80s, and apparently it's 2014 here? If he can travel through time...] If you're really him, then what year is the last year you remember before coming here?