Rio is one of the routes served daily with a 777-300ER. The oldest is only 4 years old and the newest is less than 6 months old. A wise choice sir!
Also it's a Mixed Fleet route - were the crew all young?
Despite what people think, BA do have plenty of new (<5 year old) aircraft. Sadly, with a fleet of over 250, there are always going to be a large number of ones >15!!!