New Kids in the House - S2-E10
Corrected entry: Joey stated his age as "55...ish" in the first episode, while Jesse says that Joey is 60. But in the season 2 episode "New Kids in the House", DJ is turning 39 years old. This means that Joey should be nearly 70. He was 29 or 30 when he first moved in with Danny, who turned 30 in the first season of the original show. It was established during the first show that Danny and Joey were in school together.
Corrected entry: In Fuller House we meet Kimmie's younger brother, but in Full House, there was a conversation where Stephanie mentioned in exasperation, "younger sisters" and Kimmie replied "that's why my parents stopped with me."
Correction: She must have meant her parents stopped having daughters; no "younger sisters".
Not sure this explanation makes sense. When parents "stop" after a certain kid is born, it's likely they would try to prevent another pregnancy altogether - not take a chance on what the gender of the next kid would be. A pregnancy here could have easily produced another sister... just happened that this next offspring was a boy.
Correction: D.J. was about 10 in the first season of Full House and Joey was about 30, so a difference of 20 years. So if DJ is now 39 that would make Joey about 60.