Pet question..anyone Have a Redear Slider Turtle?

I don't have one, but this is what they should be eating:

The captive diet for pet red-eared sliders should be a varied diet consisting of invertebrates such as worms, aquatic and land plants, and other natural foods. They should never be fed commercial dog food or cat food. Calcium (for shell health) can be supplemented by adding pieces of cuttlebone to the diet, or with commercially available vitamin supplements. A nutritious food readily accepted by young turtles is baby clams soaked in krill oil covered with powdered coral calcium. Younger turtles tend to be more carnivorous (eat more animal protein) than adults do. As they grow larger and older, they become increasingly herbivorous. Live foods are particularly enjoyed and add to the quality of life of captive turtles. Providing a wide variety of foods is the key to success with captive red-eared sliders. For pet red eared slider turtles you can feed them treats occasionlly like shrimp, chicken, cucumbers, tomatos, and more![

I have one named Tiko, he is awesome.

They can eat little bits of beef or chicken (unseasoned of course), carrots, bell peppers, fruit (maybe once or twice a week, not more), crickets, earthworm, lettuce, celery, shrimp, cuttlebone... they eat a big variety. redearslider.com has a huge list of what they eat on the forum (top right of the main page)... I LOVE that site. My RES (red eared slider) is a big boy and he loves beef, not so much chicken. He loves carrots, but not so much lettuce. Each turtle is different but it surprised me the variety that is safe and delicious for them.

its been a while, but i remember mine mostly eating pellets and fish, little minnows or goldfish, some plants too i think, lettuce...

They cannot eat just pellets.
How old is it?

Best to ask your pet store.

Nobody said this, but both pet stores I worked at fed them live goldfish and pellets.