Yes, apparently as in Family Sharing overview for kids and teens - Apple Support
However, Apple doesn't really say how. Have you simply tried turning it off as in Use Screen Time on your iPhone and iPad - Apple Support? If you just turned 18, try restarting your equipment so it takes a fresh look at configuration.
I don't know if the first link also implies you have to leave family sharing as part of doing this.
Failing that, ask Apple. Refer to this page for Apple Support for different countries ➔
Choose your country or region - Official Apple Support
Select your country (if you do not see your country, also look for "other" in regions; e.g., "Other Africa"), then "Choose a product". Click the "show" item under each category for more selections. If you don't see one that handles your issue then keep experimenting with selections until you reach one that gets you a chat session or a telephone call and get the representative to redirect you.