Ugh. People at pet stores rarely know anything about iguanas. By the time it's 7 years old, a healthy iguana should be over 5 feet long! Your friend's iguana probably didn't grow because it was stunted, with improper diet, heat and lighting, as well as improper housing.
Iguanas are NOT good beginner lizards. They require huge amounts of space as they get older. For example, you would probably need a cage that's 6 feet tall, 6 feet long and about 4 feet wide for an adult. Iguanas require specialized lighting, for both heat and UV light, and a particular diet. They're herbivores - I make my iguana two salads every day, with lots of dark leafy greens and other veggies. Once they get big, if they bite it can do you some real damage. It would require stitches most likely.
Also, when the males go into breeding season, there is a risk that even normally tame igs will become aggressive. You can't tell if your baby iguana is male or female until they're about a year old.
It's good that you're doing some research here before you go out to buy a new pet. Many people don't do that, and end up with large lizards that they don't know how to take care of and don't want. If you're looking for a beginner lizard, look into some other animal. Corn snakes are a good beginner reptile. I know you said your dad is scared of snakes, but corns are fairly docile, quite pretty, and they don't get as large as boa constrictors. They also require much less specialized care than iguanas do. Much easier to handle, and not dangerous.
Kate