odd, this, but my experience of Brainjuicer is almost identical to yours, with my easily earning a £5 amazon voucher in the first short while, then nothing for a couple of years....however, they might ask you if you are signed up for regular newsletters, in which you can do the topical juicer each month with three chances to win £100 amazon/cash - I have problems on my computer with the brainjuicers, however, they are by far my favourites, as they are so much fun and allow you to use your own words, and imagination. They are colourful, and isn't that little brain just so cute?!
Shortly after I complained, I did get an offer of a survey which I didn't qualify for, but received 25p for anyway, making my sum total of earnings £2.90 - wow! However, I don't know about being too old, I am only in my forties....is that over the hill???
P.S. I did receive a reply from Cedric to tell me that I was still in the active list of users/signed up okay.