Last year I learned to make a compost tea for my allotment plot from nettles as shown here: http://www.gardenstew.com/about19288.html I realised that I drink a lot of herbal tea throughout the year and was wondering if doing the same thing with the discarded nettle, mint, and rooibos teabags would make the same kind of thing, or do the ingredients have to be fresh?
Compost is, almost by definition, not fresh, so yes, go right ahead and use them. I can think of few things that are rotting in the back of the refrigerator that would not be beneficial in a compost pile. Soured milk, moldy bits off a block of cheese, some vegetables that were steamed a week ago and are now slimy, I throw anything of that sort into the compost tea bucket. Since I am the undisputable top of the household food chain, anything I reject has to go all the way to the bottom (i.e., the composting bucket) before that biomass can start its long climb back up.