Wheatgrass is fine for any grass eating tort. I do not know that a Star tortoise however likes grass. Worth a shot if it is organic and cheap (free from chemicals), but not very likely that the tort will eat it. You can get organic wheatgrass at health foods stores and it's cheaper than at pet stores. Welcome to the group! What are you currently feeding your tort?
Mine don't particularly "prefer" the higher silica grasses.. but they will eat most any grass that they come across out back. They do seem to be drawn to the dandelion, wild violets, etc. They really don't care much for "wild" strawberry leaves.
My star loves it! It's pretty amazing to see that small fellow munch up a big handful of those wheatgrass. I have also included some small slices of opuntia cactus as side dish.
Previous diet was more on tortoise pellets (mazuri & pretty pets) and hibiscus flowers/leaves.