It's not ancient Greek, but perhaps the Belisarius Saga by Eric Flint and David Drake might appeal.
The first book is available in the free library, and it's being republished in three omnibus volumes.
Or perhaps Ranks of Bronze - Romans in space.
I can't remember any explicit sex scenes in the books, but they might have faded from my memory. They're certainly pretty violent in places.
Originally Posted by purl4peace
I have an extremely bright 12-year-old boy who is fascinated by ancient greek battles -- Thermopylae is his favorite. He blew through the Rick Riordan series with each book taking him about a day to read.