In Pathfinder they have the mythic rule set. Im currently in a game where we are using these rules. I want a way to determine if someone or something is mythic. I havent found any spells or other abilities which grant this information. The only way I know of is by metagaming and seeing how different things are interacting, such as steal power which targets mythic creatures. I cant target the creature unless its mythic, so is there a way to do so thats not so meta?
There are no abilities for this, because it's supposed to be obvious by default. Anything mythic is obviously mythic:
When characters encounter the mythic, they should feel as though they've just received a glimpse into an unseen world, promising so much more if they're bold enough to explore its wonders and face its dangers. …
(“Running a Mythic Game”, PFSRD; emphasis mine)
When using mythic rules, you should be able to tell when you're looking at something mythic because the GM is obviously and clearly showing you that it's mythic. Like recognises like.
If this isn't the case and your group is just including mythic rules for the new fun powers, that's cool, but you should talk to your GM about the information gap this creates.
If the GM isn't giving away this information, they're making a mythic game unnecessarily harder, and might wish to consider house-ruling an explicit “mythic sixth sense” into every mythic PC, monster, and villain to make your game line back up with the way the mythic rules are designed to work.