Selection criteria are sometimes applied the same way regardless of an athlete's age or event - but if the years it typically takes to reach a first global medal vary a lot between events, the same annually-applied rule doesn't bite equally hard everywhere. This page measures the age at which medallists actually won, at U18, U20, U23 and Olympic/World level, for every event, so that development window can be compared directly.
This page compares every event, so the differences between them are the point. 13 events, men and women.
Javelin has one of the longest development windows in the sport. Men's javelin medallists average 27.8 years old at their first Olympic/World medal (4th oldest of 13 events), and women's 28.6 (2nd of 13) - among the oldest of any event, in both.
The 800m sits at the other end. Men's 800m medallists average 24.6 - roughly 3 years younger than javelin.
That gap adds up to several extra seasons under the same rule. From age 18, javelin throwers typically have around 9.8 seasons of development before reaching medal-winning age, against roughly 6.6 for 800m athletes.
So the same annually-applied criterion is applied more times over a javelin thrower's career than an 800m runner's. Not because any individual javelin thrower is slow to develop, but because the event itself matures later - more seasons means more chances for a season-by-season criterion to catch a mark against them somewhere along the way.
UK Athletics' own Futures Programme Selection Policy recognises this. It allows athletes outside the stated age range and standards to be considered "in exceptional cases only", including those who "compete in events with long developmental pathways".