Ignore the wings because you can't tell based on the wings with Pheasants. Look at the spurs of the bird. Junvenile (a year old or less) = light coloured spur, blunt tip and dull finish. Early in the season the spur is softer and shorter. Adult = dark coloured spur, hard, long, sharp tip and shinier.

Also don't throw away the feet. After cutting them off, prep by blanching and peeling the outer skin, then trim the nails and spurs. The prepped feet are an excellent ingredient for soup, stocks and demi-glace from which you can make the richest, silkiest gravies and can help set terrines.

Just wanted to add that if you have a choice of bird, choose the one that had a cleaner death. The flavour and texture will be affected by how much trauma and bruising it went through during the killing process. Often the undesirable "gamier" flavours associated with game is from severe bruising. It's true that meat tastes better from a lucky and skilled hunter's table.