There really wasn't any reason to be nervous about meeting Luke. Yes, he was the Jedi that took on the Empire and won and sometimes he could be quite serious, particularly about studying and training. Luke knew how to be calm and quietly intimidating if he needed to.
But really, he liked to think he was pretty friendly. For instance, he'd shown up a little bit early with both a pot of coffee and tea and then a few additional choices he hadn't mentioned: soda was excellent and that was what Luke had picked for himself.
His smile had dimples. "Finn. Hello," he greeted from next to the table in the greenhouse. No one had probably mentioned the fact that Luke was short, either.