When I did my first couple of games, I told the managers I was newly qualified. These were all OA mens games as well.. Whilst I got a couple things wrong, even I admit on my reflection back then, the players and managers were actually quite accepting of me.
I've refereed them since, and we mostly have had a good relationship, including them asking me to cover friendlies during preseason.
Now, after doing some youth games, if they were my first, I think I wouldn't have told them. Managers in youth tend to find any excuse to put the blame onto you. I've had a lot more issues with youth managers, than I've had with OA players.
OA players may give abuse, I may sin bin them for dissent, but I've had them come to me after the game and buy a pint to apologise.