Swarmkeeper
Hero
Plenty of 8 years olds learnt on B/X as well it's an anecdote.
B/X is objectively easier to run what you prefer is subjective.
AD&D is alot more subjective.
Hell you can look at pagecount around 1000 for 5E core books around 100 for basic or 300 for BECMI Rules cyclopedia.
There's just less of it ergo easier. Less options as well. What you prefer is up to you.
Easiest D&D to run is the clones with ascending AC but I haven't tested out new clones like OSE more things like Basic Fantasy or Castles and Crusades.
But what about the 5e Basic Rules @ 180 pages? That's all you need to play...