I dug out a book with pics of various corn morphs, and the photo of a snow corn they have has pinkish red eyes. I don't know if it's normal for that morph, or just normal for that one specimen, or if the photo just had redeye glare. You can probably websurf and Kingsnake has links to breeders with pictures of many different morphs.
Garters are very lovely and underrated creatures. They're hardy and incredibly graceful. Active, alert and fun to watch. However they're fast, skittish and generally eat fish. Corns are larger, slower moving and calmer. They're both worth a shot as a first snake so it's really up to you.
As for baby, juvenile and adult, they each have their advantages. As long as the snake in question is healthy, good tempered and eating ok, it's pretty much personal preference. Babies are cute and you can watch them grow, but they're kind of squirmy and delicate. Juveniles are but less delicate and in theory, they're well started since they've grown from babies. With adults, the advantage is you can be certain of what you'll get, temperment and colorwise.
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0.1 chickens (Condor)
0.2 dog mutts (half ownership, only mine when they misbehave, Lucy & Amy)
0.1 Halflinger horse (Crissy)
0.1 Normal phase California Kingsnake (Sophia)
1.1 parents
Still searching for 1.0 WC human