I've got a guy from my work who used to play OAD&D way back in the day who I've invited to play a 1-shot with me and some folks from my regular Rise of the Runelords group. I've talked about the big changes between what we play and OAD&D and he's looking forward to it.
I feel like something between lvl 8-12 would be a good range for him to get a feel for what the game has become, but I'm wondering what would be a good adventure that really evokes the tropes of Dungeons and Dragons.
I'm open to converting from 3.5 or even 4e (the story is what I need. I can remake monsters and enemies).
From someone who has played every edition of d&d, I'm taking some old school dungeons and converting them to Pathfinder. It might go over easier if he recognizes the module (or seems familiar).
Failing that you could just take the core idea and whip up a smaller version of it. Just make sure you have all the elements.. combat,a few skill challenges and a thinking/puzzle event.. throw in a little drama with a couple of role-playing scenes. Keep his character in the basics as far as class options are concerned and he should get the system down. The biggest difference imo are skills. Before each class had their own set of abilities.. now it's based on player-option.
As far as level goes..stay with something between 4-7. You get decent options and still get a few advanced ones regardless of race/class combo.
A simple kidnapping with a couple of bandits/thieves or a missing villager who wanders into the abandoned castle/ruins/temple should do. Add in the the nearby wizard or priest who lives alone to dispense advice or low level magic item and he will feel right at home.