Nymphetomania

[Achebe]

Nymphetomania

The scene: a reincarnated Millais looks at his former pictures, dreams of his former muse....

There's few years separating these two lovers,
five and fourteen and a hundred blend together
as easy as blood and water. But look no more
than twelve years later, when all the youth
he once loved in her's gone: the rosebush wilted

at the unnerving mixture, got switched
with a self-destroying hunger. Now, he dreams
of days when girls were younger -- he's choked
by that raised chin, by those tremendous eyes,
by the pale fingers he hopes will crack "I crave you".

I don't know if you need the reincarnation. The poem could work as well if Millais was just looking at the paintings at any time in his life. Slightly less mysterious.
The first painting, wikipedia tells me, was in 1857. The second, in 1880. That's 23 years, not 12.
Also, Sophy was 14 in the first one. That doesn't make her a nymphet strictly speaking.