Result of a chat with  darkmatter07 x3
Derek is from G4, Nicolás from G5, but here both have about same age x3
And yes, Derek is 8 cms taller than Nico. Is a tall, very athletic boy, and he goes to swim very often with her cousins Dora and Kurfust, plus his swimming teacher job, so stays in shape very easily

remember to check the amazing digital Derek fanart! https://www.furaffinity.net/view/37153398/

and, for the new ones here, Derek started as a Dora´s rule63 design https://www.furaffinity.net/view/30759438/ but i liked it so much that becomed cousin of the younger Klendathus x3