Your game is fine, but I feel like the dog character looks too old for the protagonist, and that makes the game less visually appealing and a little disgusting.
You do have a good point here, the first thing I thought when I saw this vn was exactly the same thing you are writing here
Sooooo, I found out that, if you want a furry to look old, u can give him a moustache in the snout, somehow, that makes it look old, and, you can take it further if you paint the snout (and if you want, the jaw too) white/grey
Now, does David share these points?
Yep, he does
Here's a little example of the point I'm trying to make here :D

Also, his coat looks like something a grandpa would use trying to look cool with the young xD
Heck, I think it would be really funny if in the vn David had this problem when he meets new people
Eh, I don't think that's a problem, Ranzo from Dawntide (awesome and marvelous vn, almost everyone should check it out) has the same type of hair, I even think David and Ranzo are the same breed (Schnauzer)
Here's an image of the dawg in question:

Idk how, when, where, and why, but, Ranzo shares some points in the "why does a furry look old?" thing we got here, and somehow to me, seems like a 20-30 year old
I would say the color in the snout is the one making us think he's old, but, yeah, his hair just grows like that, he could just go to a barbers shop and everything would be done, David just doesn't do it because (reason goes here)
Even so, I feel like in a furry world type of setting, it would make a good plot point, like, maybe it would be a little silly issue the character has to bear or, a deeper insecurity eating the character little by little..
Idk, I think I should just make a vn by this point, I have a lot of ideas and it sounds fun, anyways, see ya, thx for reading and have a good day (or night), stay safe out there :D