He looks very safe and easy to ride, and his jumping form is quite good, even over those low fences. He has his changes, though I think the first one was late behind (awful in dressage but not a deal-breaker for an eq-hunter). He looks like he's been a very reliable Short Stirrup-Equitation packer and has been there, done that, and has the ribbons.
Video doesnt show much trot, and the little bit in the beginning looked a little ouchy to me.
Which brings me to his age. He has every right to be a bit stiff at 17, especially if he is jumping a lot. 17 is getting up there, especially for jumping horses in terms of soreness/soundness. I would find out if he's on any maintenance products. Would you do a PPE? (I would, but I always do) There's lots of stuff you can do to make the oldsters more comfortable.
I also cant help but think that $2K is a bit steep for a 17 y.o. pony, though if he has a proven show record and/or is a valued school or lease horse, then I get it.
I think he's cute, have fun trying him!