Being cautious about one's finances isn't necessarily a bad thing. I didn't go on my first vacation until I was 33 because I wanted to get my own financial house in order first. If he's not comfortable, then I think you should respect his decision. If you want to get him a small souvenir or something from the trip, I'd probably ask him first. Just let him know that the door is open. If not this time, then maybe he'll be more accepting the next time.