In Patroclus and Achilles' case, Achilles would have been the younger as Patroclus is usually seen as his elder.
ɪn pˈætɹɑːkləs ænd ɐkˈɪliːz kˈeɪs, ɐkˈɪliːz wʊdhɐv bˌɪn ðə jˈʌŋɡɚɹ æz pˈætɹɑːkləs ɪz jˈuːʒuːəli sˈiːn æz hɪz ˈɛldɚ.