It's the same as it's been since Windows 95: the StartUp folder would not show AVG in any older systems either. That's why there's the alternative.
Type the word msconfig into your Start menu, then press Enter. Just like Windows 95 through XP: this will let you uncheck Startup items.
If this was helpful, please vote by clicking the green triangle. If it solves the issue, click Propose as Answer. Thanks!