Later Casanova portraits
The portrait of Casanova below is said to be around 1788 when he was 63 years old and living in Bohemia at Dux (Duchcov). It is an engraving that appeared in the front of his only work of fiction, Icosameron (1788), a long and rambling utopian fantasy which had the helpful sub-title of "Or the Story of Edward and Elizabeth Who Spent Eighty-One Years in the Land of the Megamicres, Original Inhabitants of Protocosmos in the Interior of the Globe." It was first published in English, belatedly, in 1986.
Below is a possible portrait from around 1774 when Casanova was almost 50. It's a photo dating back to the 1930's of a painting by Venetian portrait painter Alessandro Longhi.
The Toledo Museum of Art claims this portrait by Alessandro Longhi circa 1775 is possibly Casanova.