So far, so good. I'd get him a nice grey upholstered headboard to accentuate the bed and hang some artwork with black frames and some red and other colours (on the grey wall). That would make a big improvement.

We did a Nationals baseball team theme for one customer's son's room. The room was painted in one of the team colors above char rail height and another team color below. The two colors were separated with a team wallpaper border. It really turned out well. The team colors were available from Home Depot.

Personally, I would prefer to have bead board wainscoting in the grey and the upper walls in the rich red. If wainscoting is too difficult, just install a white-painted chair rail about 40 inches from the floor. Then, paint the lower wall the grey and the upper the rich red. I would suggest you find a plaid that has black, grey, white, and rich red in it and use this plaid for the bedspread(s) and curtains. If you son has a favorite team with colors that harmonize with or accentuate the grey and red, use colorful team emblems, photographs, and baseball memorabilia to accessorize the room.