I think they just grow at different rates, he may just mature faster then some. Hard to know how big he'll get, they do have quite a range in size, and he definately looks purebred.
I don't give in to Hilda if she squeals at me, to me it's like a kid throwing a tantrum, thankfully she's not much of a squealer, but she does occationally try to get me to feed her more often. She's still getting baby milk and cereal (so far she is turning her nose up at real pig food, but it's there when she's ready). If she asks early, or gets to insistant for her food I ignore her and she eventually gives up and takes a nap, that is when I'll feed her. I also don't let her go if she squeals when I hold her.
As for toys, it's been forever since I had one, so I'm really only going by what Hilda likes, but she likes to play w/ stuff, so I'm sure Horton would love some toys! I'm going to see if I can figure out how to put a video on youtube to share, but I've got a few of Hilda playing, in one she's grabbed a plastic bag I put some trash in and she's running around the room w/ it in her mouth spilling trash everywhere, she even shakes it like a dog. The thing she likes best though are stuffed animals, she attacks them, biting and shaking and jumping on them. She also enjoys pushing her bowls around, at first I figured she just wanted me to fill them, but I think she really enjoys pushing them, so I'm thinking she may also like a ball she can roll. I just ordered her some stuff toys of her own, so we'll see if they are as fun when they're hers!
As for the water (and I think you were asking redhen these things, but I'm sure you don't mind multiple answers), the only trick I can think of for the water is fastening it to something, otherwise he probably just enjoys knocking it over.