He met madara before... im guessing around the first ninja war time.
From the way he looked...im guessing he was maybe around his twenties?
Time flew by.
Madara met obito when he was close to his death...not to mention he got an extension of years from gedou mazo.
I'm guessing oonoki should be around his 60-80's by then.
And years passed and now obito is older.
So shouldnt the old fart have been dead by now?