I haven’t used Yahoo as a general search engine since an American friend introduced me to the miracle that was Google in November 2000, but I do use Yahoo Finance for share price data, and the clunky BT Yahoo email service. All this points me to one conclusion: Yahoo is as middle-aged as I am, and the decision by hot new ex-Google chief executive Marissa Mayer to seek brand rejuvenation by buying the unprofitable blogging site Tumblr for $1.1