AITA for "belittling" my (22F) sister boyfriend (45M) for not-explicitly rage baiting him
I am a (23F) and my sister "Allie" is a (22F). She has been dating her boyfriend "AJ" (45M) on and off for 2 years. They have known each other since she was 19 when they started work together. Because of his age, I had been sketched out by him. My sister is young and sometimes immature so I thought it was weird that a man in his 40's who has 3 kids would pursue her. (His oldest daughter is 17). But I still support my sister, so I went with it and was never direct with my feelings to Aaron himself. My sister is pregnant with his fourth child. I was pretty upset about this, she just turned 22 but I told her I would support her and the baby as much as possible. I have planned my PTO around the birth to take off work for 2 weeks to help, as Aaron has two young daughters to also care for. I feel like I have to walk on eggshells when I talk to her now, as everything I say seems to upset her. I thought we had moved passed this when I reiterated that I was going to support her decision to keep the baby. Until a week ago, I wake up to a very long angry text about how I should apologize to Aaron for "belittling him" at Christmas, it is currently THE END OF MAY.
To summarize the events at Christmas, on 12/26 we went to AJ's house for dinner, where my sister lives now. We arrived and it is a nice house, FL ranch style. My boyfriend, mom, and stepdad are in the car. I'm looking at the house and am thinking something is missing, then oddly enough I said "where are his gutters?" Just an observation that I made and my family also thought. When we went inside, I greeted him hello, gave him a hug then asked "where are your gutters?". He chuckled and said he didn't have them, then we moved on. I never said anything else about his house. After dinner, we are standing around when we start talking about Christmas presents. I mentioned I wanted to get this fun book for all my girlfriends "how to shatter a fragile male ego". It has funny phrases such as "you look like you wouldn't go camping". I would buy it as a gag for my friends. Even my boyfriend thinks it's funny and not serious. So I explain the book. As examples, my boyfriend says the camping one, then I say "you look like you wouldn't be a fast runner" AJ replied "yeah well I run a mile in 6 minutes, what do you do?" I flipped my hair coyishly and say "I don't run" to which he replies "yeah looks like it!" Well I am plus size, and my family gasp and say Aaron! We laughed and moved on. Allie texts me later and apologizes, to which I reply that we were just goofing, and I moved on.
So it is now May and Allie texts saying how AJ is upset about how at Christmas I belittled him and made horrible comments about his house, and how he does not like me at all. The only way I can repair and move on in my relationship with my sister is if I apologize to him when I see him in person next. Reminder, AJ is a 45 year old man with baby #4 on the way. I'm 23. Am I the asshole for belittling him and should I apologize?