In the game there will be enemies and the player will kill them and vice versa. I want to create something that everyone can enjoy it, I don't want o limit my game to mature adults.
I can safely say that as long as your game doesn't involve excessive amounts of blood and gore, you're not.
What I mean by that is that, in my opinion, people don't give kids enough credit. Children are much more resilient than people think.
Super Mario games are pretty good at that because they never face any restrictions.ever say never. Some designs for Marios water gun in Sunshine was scrapped because it was too controversial for the US. But still, yeah, that's just one of many.
However, depending on your definition of violence, there's a fair amount of violence in games about/including Mario.
(New) Super Mario Bros - Jump on (and crush) enemies.
Mario 64 - Punching and Kicking
Smash Bros - More Punching and Kicking, this time it's the entire point of the game.
Super Mario RPG/Paper Mario Series - All of the above and more.
But the common thread is, it's all cartoony violence. There's no blood, no gore, but it's still violence. And they're all considered fine games for children to enjoy.
Depending a bit on the age group you could have more or less violence in your game. Consider this; the Smash Bros series has had the followiung PEGI ratings: 7+, 3+ and 12+. Not only does it vary wildly between the different versions, but it varies just as much between regions. In Japan Brawl had a CERO A rating (All Ages) while in the US it had an ESRB T rating (Teen).
In short, if your violence is cartoony and/or slapsticky, I'd say you're fine.
If you really don't want any violence in your game, but still want conflict, then another method of conflict resolution is likely what you want.