Why the roof of my mouth looks greyish? Its always been like that I thought it was oral cancer im 22 but don't drink or smoke

Dentist examination. Are you anemic? You are not likely to have oral cancer. The greyish color may be due to anemia. It would help to examine your mouth and your doctor or dentist could do that.
Csndidia. There are many reasons why the palate can look lighter. One is years infection or candidiasis. Another is lower vascularity or thin gum tissue so the roof of the mouth appears less red. An oral surgeon or an oral pathologist can determine it it is a problem.
Likely normal. Any coloration of the skin (or mucosa, in your case) that does not change over time is most likely normal for you. Nevertheless, any time you notice any new areas of pigmentation or changes in coloration you should discuss this with your physician. You might also ask you dentist to look at this.
Best to be. Seen by your dentist to make sure there is no problem. The mouth is dark inside so without proper illumination it might have a different appearance. But best to be checked out.