Even the style of show I seem to get that feeling. There were a ton of plots that focuses on kids for kids near the end. Season 1 for sure didn't see that, and even the next couple years it had a lot to do with the interacting of the family unit more than anything. There were a lot of episodes with the girls by that time, but I do think an older audience would be able to connect to those ones earlier on than the by the time the series was coming to an end.
As I see it, the major divide in that respect was between seasons 4 and 5. Season 1 was mainly about the guys tring to make their unique living situation work. Jesse and Joey's advertising career in seasons 2-4 was very adult in contrast to their later jobs. Also, Jesse and Becky's relationship had a more adult feel in seasons 2-4, before it became focused around starting and then raising a family of their own in season 5-8.
For the girls, their plots in the early seasons had a greater focus on the family unit. Common themes in the early season plots for the girls involved trying to get the guys to allow them to do something; getting into trouble that the adults would step in and fix, even if the girls didn't want their involvement; and fights that the guys had to step in and mediate. Then in the later seasons, more of the plots for the girls became focused away from the family unit. The stories often dealt with problems that were worked out between the girls and their friends. The involvement from the guys most came mostly in the form of advice. When the guys did take on a greater role in the girl's problems in the later seasons, it was often at the request of the girls.