At seven, he's old enough to be taught how to handle the pig. But they're very skittish, usually don't like to be held, and WILL jump out of his hands/arms unless he's very careful. I always made our 7-year-old sit when she was holding the pig until I was sure she knew what she was doing.
Whether you need to put the lid back on depends on how much you trust your son and whether there are other animals in the house that might get in the cage.
She needs unlimited long strand grass hay ALL the time -- timothy, blue, orchard, meadow, brome. Keep the hayrack filled.
At seven months, I'd restrict her to no more than 1/4 cup of pellets, and cut that back to 1/8 by the time she's a year old. But you have to watch to make sure she isn't ignoring the hay and the vegetables, which are more important in the long run than the pellets.
An adult guinea pig needs a cup of vegetables per day -- your pig could probably do with 2/3 cup. Red or green leaf lettuce and bell peppers should be the staples. Read
https://www.guineapigcages.com/foru...y-nutrition-charts-poisonous-plants-list.html for what you can feed and how often.
I feed mine vegetables three times a day, and fill their pellet dishes once a day. They do get occasional treats throughout the day, because my husband can't bear to pass the cage without giving them something. I try to make him limit the fruit, but they get dill, a basil leaf, a cilantro sprig, or something non-sweet that we've got in the fridge.
