Every case needs to be judged on it’s own merits, of course, but if as TD I got a complaint from a player that his opponent was annoying him and/or distracting him by fidgeting uncontrollably I would probably warn the player not to continue doing so. The age of the fidgeting player would be irrelevant. The only exception would be someone with medical reason, like Parkinson’s Disease, that would make it impossible for the player to desist from fidgeting.