Hair; a child's sense of wonder; tolerance; car keys. Just a few of the things that you start to lose as you grow older. Another is the capacity to have heroes, at least in sport. For many of us, that means football heroes.
As a child, my heroes were the warriors who played in Liverpool Football Club's red every Saturday and Wednesday. In a more innocent age, I knew very little about their personal lives, and cared even less. Kenny Dalglish, Ian Rush, John Barnes: these were supermen who scored goals and lifted trophies. They made us happy, and our love for them began and ended with their exploits on the field.
But then you start growing older, but players stay the same age. And we all know what grumpy old men think of kids these days.
Admiration is slowly replaced by cynicism. And, ultimately, contempt bred by the realisation that these millionaire sportsmen whose salaries you've helped to pay for years are nothing but money-grabbing parasites who care far less than you do about the club you would pay to represent for even one fleeting moment.
Defiantly, inexplicably, even stupidly some might say, this only succeeds in strengthening your bond to the team you support. Less hero worship, more blind faith.
The American comedian Jerry Seinfeld a little cruelly joked that sports fans end up cheering for nothing more than an item of clothes, a shirt. He is, in a sense, right; but he's also so, so wrong. Fickleness and loyalty are two sides of the same coin.
Today, the proliferation of football coverage and social media has changed how we perceive sports figures even more. Barriers between players and fans are slowly disappearing, and with them, perhaps forever, our hero-worship. The players now reveal their innermost thoughts to the public without the barriers of PR teams, and the public in turn can tell them how useless their performances were at the weekend.
Footballers pre-empt the tabloids and the paparazzi by tweeting their own holiday photos. Last summer, Manchester United's prolific striker Wayne Rooney posted a photo of himself with Liverpool's somewhat-less-prolific forward Andy Carroll. The 13-year-old in me strongly disapproved of such fraternising with the enemy.
Several recent incidents in the usually partisan world of English football have brought the notion of the hero into clear focus.
First, came last year's suicide of Wales manager Gary Speed at the age of 42. Then Fabrice Muamba's horrific collapse from a cardiac arrest at White Hart Lane last month.
And on Monday, Aston Villa's immensely popular captain Stiliyan Petrov began treatment at a London hospital after being diagnosed with acute leukaemia. Suddenly, football, quite rightly, had its priorities in order. At least temporarily.
Certainly, some of the reactions, and tributes, to these incidents gave the impression of being forced, bordering on mawkish. Writing in The National yesterday, Will Batchelor wondered whether genuine concern for the players was being overplayed.
Not even the most cynical of fans would have been unmoved by these men's plights. But, as Batchelor noted, the slogans were unnecessary, and have set a bad precedent.
"What about players laid low by depression, diabetes, dialysis?" he asked. In appearing so heartbreakingly human, like millions of sufferers around the world, these men became real heroes for all to see. The issue did not need sign-posting.
Still, this new-found collective conscientiousness probably won't last. Kids will soon get back to cheering on idols with feet of clay. And shirts bearing Rooney, Drogba and even the anti-hero himself, Tevez, will continue to sell in the millions. The cynics will cheer the team, and abuse the player.
Some of us will even continue to support poor Andy Carroll. Well, at least his shirt, anyway.
On Twitter: @AliKhaled_