Русско-английский словарь пословиц и поговорок
СЕДИНА В ГОЛОВУ, А БЕС В РЕБРО
Не is an elderly man but started a love affair at his age. (This is said ironically.)
Cf:Grey hairs are nourished with green thoughts (Br.). /There is/ no fool like an old fool (Am.,Br.). /There is/ no fool to the old fool (Br.)