What happens to all those "older developers" when they reach the ripe old age of 50? (or 40) Surely, not everyone makes enough money to retire at 50. There can't be enough management positions for everyone either. So, where?
Almost everyone with a professional job makes enough money to retire at fifty - the question is whether their expenses are low enough to do so. Save 35% of your salary and you can retire in 25 years. Save half your salary and you can retire in 17 years.