My account thinks im a child

Xbox account age can not be changed as it is permanently connected to the first date of birth entered when creating your Microsoft account. This can't be changed even by Xbox support. Your account will be promoted to an adult account when that original birth date reaches 18 (20 in Korea and Japan). You can change your Microsoft account age but that doesn't change your xbox account age. If your Microsoft account is an adult account you may be able to access the page to change privacy settings but any changes will not take effect for real if your xbox account is a child account.

You will need an adult to create an account, invite you to a family group and change some privacy settings for you.

https://support.microsoft.com/en-us/help/12417/microsoft-account-add-members-to-family

Have the adult on their adult account go here https://account.xbox.com/Settings and click on the child's account and allow the option on the first page called "Share stuff people make (Xbox 360: Member Content)" to everyone (must be everyone). Also, on the first page, "Others can communicate with voice, text, or invites" to Friends or Everybody. And on the xbox one/windows 10 tab the second option down, "Join multiplayer games", enable that. And then log out and in on the account in question on the console/device and that account can play online and have that problem solved.

Yes keep in mind that while the system lets you change your age anytime to whatever you want. It's not recognized as a new date of birth. This is to prevent kids from changing there ages just to bypass things 

Hi

I literally just want to [...]change my profile picture to a custom one but [...] it says that i need to be older to do this. [...]My account is clearly over 18, I have changed all settings to where i shouldnt be affected by this 

The "adultness" of an account isn't determined by the settings you change. 

During the creation of your account you are asked to provide a birthdate. That birthdate determines the age of the account, and only if according to that birthdate your account turns 18 (or 20 in Japan), your account truly is an adult account. 

Until then your account is a limited Child account, even though your parents might set your account to allow certain "adult" features like talking to strangers or buying stuff. 

Changing your Profile picture is unfortunately a thing, only "real" adult accounts can do, and there is no setting to circumvent that.