Some people say you can tell from the shape of the head and colours around the tail but I've always been told a DNA test is the only sure-fire way of finding out.
Cardboard, old toy pieces wrapped up individually with paper & put in a toy bucket hanging in their cage. strips of cardboard or paper strung thru the bars. Just some ideas
They are really adorable. Red factor is rare, but itcan grow out & they will be the same color as a grey, They don't usually keep the red factor, so its not worth paying more for. They look healthy!
Macaws are a little easier to visually sex by the rounder female head vs slightly flatter male head top, imo.
But the easiest parrots to visually sex are the Eclectus parrots. lol
DNA sexing is the best option for a youngster. With a mature female parrot, well, the laying of an egg is sort of a giveaway.