Corrected entry: In the scene where Derek first meets Odette and gives her the locket, Derek looks much older than Odette but when they are at Derek's castle they look the same age.
Corrected entry: When Derek and Bromley are playing "Catch and Fire", Rodgers ties the apple on top of Bromley's head and then puts the helmet on Bromley. When he puts the helmet on him, the apple magically ends up on top of the helmet with no evidence that the helmet had a space to facilitate that.
Correction: If you watch the helmet, you can see on two occasions that there is a hole in the top for the apple to go through (one before the shot, one after the helmet falls to the ground). It's a small hole, but within reasonable suspension of disbelief for the style of cartoon.
Correction: In the beginning I agree Derek does look older but when they meet at the castle Derek still looks older than Odette and throughout the song as they grow up you can tell Derek is older.