If you do use any topicals on your tortoises' shells, be sure to polish off the excess with an absorbent cloth. If you leave a bunch on the shell it attracts dirt, which could lead to overheating. Also, olive oil MIGHT attract ants to your tortoise.
I used it once on my guys and it made them all nice and shiney but they stayed that way for a long time and I got a little uncomfortable about it. I like them dirty and not so shiney better, you know, like a tortoise should be. It is, however, good for scrambling eggs and cooking mushrooms and goes well in a light spaghetti sauce with some garlic and onion.