ageless(continuing infinitely or indefinitely) adjective [UK: ˈeɪdʒ.ləs] [US: ˈeɪdʒ.ləs]
eternal(lasting forever) adjective [UK: ɪ.ˈtɜːn.l̩] [US: ˌɪ.ˈtɝː.nl̩]I believe in eternal life. = Creo en la vida eterna.
protracted(lasting for a long time or longer than expected or usual) adjective [UK: prə.ˈtræk.tɪd] [US: proˈtræk.təd]
undying(permanent; never-ending; infinite) adjective [UK: ˌʌn.ˈdaɪ.ɪŋ] [US: ən.ˈdaɪ.ɪŋ]From that moment on, he felt undying hatred for his oppressors. = A partir de ese momento, sintió odio eterno hacia sus opresores.