The Holy Grail of American Sport. Body armour, helmets, full contact sport – The American Game Having won three Super Bowls, been four times ‘All First Team All Pro’, Rob Gronkowski announces his retirement at the great age of – wait for it – 29 years old! What! 29 nine years old, wow! Maybe it’s the word ‘retire’ that catches my eye. I’ve been on-line trying to research the different ages people can play professional sport at, and for that…