From the standpoint of wanting horses to stay as sound as possible for as many years of work as possible, I *like* the condition he's in, compared to an awful lot of what's been for sale in the last twenty years. (Well ok, he could probably use a couple good wormings). When you feed the bejeebers out of yearlings, especially with TB and/or draft background, you may get an extra couple inches of height but you get joint and soft tissue problems as well, like as not. Horses, especially largeish horses, are not supposed to grow explosively as babies, they are supposed to put on good structure first and *then* weight, and at a moderate pace. I truly, honestly believe that what you're looking at in that picture is not malnutrition (which does weaken a horse in the long run), it's *appropriate proper* growth, which many people are not so used to seeing in this day and age, alas.
I'm not impressed by his hind end but on a tb/clyde I would not expect it to be too limiting to his jumping ability -- he's a questionmark for the higher divisions, but frankly most horses from most bloodlines you just have to wait and see for that anyhow. It's not actually dysfunctionally built or anything.
The neck is not Warmblood-high-and-arched and never will be; no matter how you feed and exercise him, he'll look like an older-style (like pre-1980s) type hunter, but, so? Those are good horses too
The only thing I am kind of skeptical about, on him, is the length and set of pasterns. I would really like to see them a bit shorter and his feet more *under* his legs. On a grown horse I'd say that construction would augur poorly for his long-term soundness over fences; but it is less 'fixed' in young stock and honestly it has been long enough since I looked at a whole lotta TB yearlings that I don't 100% trust my judgement on it here. If you can see his sire and/or dam and their pasterns/feet are where they should be, that would be an encouraging sign.
Really, overall, the way he looks and with mostly-TB-a-little-Clyde, he should be able to go 3' no problem, beyond that who knows. A little draft blood in a mostly-TB almost always makes a very nice riding horse, IME. So if he has a good temperament as is currently sound and you can afford to store him somewhere for a couple years til he reaches useable age, then I'd say go for it.
(Although, for what you'd likely spend keeping him for a coupla years til you can do anything with him -- and with *any* draft blood in the mix, I'd be extra conservative about when to start him and how much work -- it seems to me that you could probably buy just as nice a horse of startable age and KNOW he's made it through those years safe and sound. Still, if you want a yearling, this is as good an affordable prospect as any, IMO)
Good luck, have fun,
Pat