I'm going to make a joke about my wife being old on her 30th birthday
Do you think that's funny? What makes you want to mock your wife on her age?
She really is old. I can't help it.
It is never right to get a cheap laugh at the expense of your wife. Just because you're kidding doesn't mean that she can't feel hurt from your words.
I guess that I should stop making such rude jokes to my wife.
Good, you should stop mocking her and I'm glad that you're starting to take your wife's feelings seriously. You two will have a great birthday together.