It depends upon whether you have registered or filled the online application form for JEE Advanced examination or not. If you have qualified JEE Main and also registered for JEE Advanced but not given it, then your attempt will be counted. And if you have qualified for JEE Main and not filled out the application for JEE Advanced then your chance is secured. You can give JEE Advanced next year. Although, it is not necessary to appear for JEE Advanced unless you want a seat in IITs. With a good rank in JEE Main, you can easily get NITs and IIITs. Hope this helps!

No, If you don't appear JEE Advance after JEE Mains, it won't be counted as your attempt. But you shouldn't register for the Advance then . Once you register for the Advance ,it will be counted. So, if you don't wish to appear the Advance exam ,don't fill the application form. Though you don't have any age limit, you can attempt advance 2 times consecutively..