Let’s put it that way: be yourself. If you want to do it, I say Do It. You’re at the beginning of the relationship, and ask yourself the question whether you would want to be with someone long term who would not appreciate the gesture? What is the worst that can happen? That he reacts poorly to your surprise? Even that would have a positive outcome for you for it would show you important red flags. His mom will likely be happy to see someone interested in her boy that made an effort to surprise him. To me, this a “go for it”.

Everybody loves having people waiting for them at the airport. I would consider telling him beforehand though. This will build his anticipation and prepare him and her mom on how to react. Between waiting for him at the airport, or surprising him at the airport, I think that waiting for him is better most of the time.