Old Tom, Allan Robertson, Jamie Anderson - with their caddies - 1850
The 'notion' that professional caddies or other grown men have ruined caddying for kids is just that, a notion.
I can think of several other factors, like the advent of carts; labor (in CT. you must be at least 14 and can only caddie at private or municipal courses); legal (you can't contract with a minor); insurance ( including the liability of the player, especially with youngsters); pool (how many youngsters
want to caddie, or for that matter, learn the game); etc..
....and until remote walking-only courses build dormitories and hire den mothers you'll be stuck paying adults to carry your bag.
...and the Brits started charging admission to the Open in 1926.