How many times have you seen this horse before? Is he usually stiff legged...The way you worded it seemed to me that the girl riding owned him this is why I asked how often you see Devon..
My friend owns a 9 year old whom gets stiff front legs, and she moves around sloppy I guess you could say, She even canters around by her self straight legged not bending at the knee in the front legs... Her case is she doesnt get worked enough, and it depends on the horse whether their tendons will stay streched and supple for months after not being exercised and streched out, but with her mare and maybe in Devons case, after a while of no exercise (trotting, and flexing I mean mainly) their tendons shrink back up(i'm bad at words) and do not stay streched and loose, causing stiffness....Now again this is only my experince in stiff legs and may not be the case for Devon.
If this is Devons problem, that he doesnt get exercised enough, it may cause problems with tendons later on if the rider just hops on and asks him to do alot of work before properly streching him out....
This is what we do with the mare that gets stiff legs, after a while of not riding or any exersice, before we tack up, we pick her legs up and stretch them out in hand, massage them gently with our fingers and then put work boots on her, when we get on her we get her to walk the arena 2 times, stop her and flex, get her to touch your toes with her nose 2 times on each side, have her diengage both ways, then walk her out, then do lots of trotting, this will be the best to get the tendons streched out...Do as much work as you can at the trot(build good muscle tone as well), LOTS && LOTS of trotting, as many days as you or the rider can, after like 3 days of this there should be no stiffness, then we just trot everyday around the arena twice before anything else just to keep the tendons supply....
Thunder 9yr. black Mustang Appy/Paso
George 18yr. Red roan QH
'Grab life by the reins'