Two of my turtles are 11 years old, and the third turtle is 20+ years old. The 20+ year old is 11 inches long, and the other two are around 6 to 8 inches long. Their habitat is indoor.
Every morning my three RES get a head-sized portion of their food. We don't have a set schedule in terms of what we give them, but the staple is romaine lettuce.
Every other day they get romaine, or carrots, and on non-romaine days, they get a few berries, usually strawberries and/or blueberries. A couple times a month, we give them head-sized amounts of cooked chicken or turkey cold cuts. During the warm months when fishing season starts, we substitute the chicken and turkey for live nightcrawler worms, the large ones that people use for fishing. We'll give the nightcrawlers once a week.
We don't give treats or use commercial turtle pellets, or pellets of any kind.