Q: how to eliminate "items contains age-restricted material" message

Sounds like you have parental controls enabled. Here's how to manage these restrictions in iTunes:

iTunes: Using Parental Controls

http://support.apple.com/kb/HT1904

This isn't the same thing. This happens when installing apps on the iPhone or even updating apps. I get it on a certain app myself. I don't think there is a way around it.

This is surely legal protection for Apple &al

I'm sure Apple could work another way around this, but it would take a lot of people writing to them,

sending feedback: http://www.apple.com/feedback/itunesapp.html

Something like this:

"Is there not another way around avoiding the constant notice pop-up message of 'age-restricted material' when downloading and updating certain apps?

A declaration that I am the sole users of the PC and iTunes and have no children, for example.

Or simply having iTunes remember my choice of accepting these apps. (and stating "this notice will appear once - you can reset this in settings if you no longer accept the term"  or something simple like that.)

Excellent suggestion. Here's what I just submitted to the iTunes feedback form:

Please allow adult users of iTunes to eliminate the continual pop-up message of "age-restricted material" when downloading and updating certain apps. I recommend adding the permanent elimination of this message as an option in the Parental Control Preferences in iTunes. (If necessary, users can click "agree" on a legal document that certifies the user's age and the sole use of iTunes on any given computer.) Another option is for iTunes to remember the user's choice of accepting these apps.