Should I hold my son back for 4th grade

The cut-off in my area is December. My child started kindergarten at 4 and did not turn 5 until November, so he's the youngest in the class. Now he's only 9 in 4th grade.

My son had a very difficult time in 4th grade. He did poorly in science and writing, and his writing skills are below grade level. Although he scores high in word usage and his math is quite good,
his spelling and writing skills are poor. His reading is on or slightly above grade level.

He has a difficult time retaining information unless he hears it more than once.
His attention span is not very long,
but there seems to be no learning disability.

I am considering having him repeat 4th grade. He may need another year developmentally,