When an older (typically post-menopausal) woman says, “I don’t need sex,” she is 5h1t-testing you. She is obviously considering having sex with you. Reply with something playful like, “Nuns are sexy,” delivered in a playful tone with a wry smile. Or, look her up and down with the same wry smile.
Older women have lower testosterone levels and don’t feel a need for sex. However, they still enjoy and frequently seek the attention and desire of attractive men. So, in one sense, saying “I don’t need sex” is simply a ruse, even if on the hormonal level this is true.