I think you're likely right because most of the Fraggles we see in the show, save a handful, all look about the same age. There could be a lot of difference in age between them, but it doesn't appear to be a big thing to them, especially since they don't seem to have a sense of time in terms of years but rather seasons.
Hmmm this is an extent question and if you look at from a psychology point of view (with the size of the Fraggles showing their ages) I'd say Boober is the youngest of the group but seems older possibly due to being the oldest in his family. Mostlikely had a couple younger siblings which is way he always seems to feel responsible for those around him. Followed by Wembley who was probably the youngest (it always seems to be hard for them to grow up as quickly). Babies of the family tend to take longer to move out on their own or tend to live with a friend or family member for several years after "moving out". Followed by Red who was probably a middle child in a large family, she seems to throw off that "look what I can do" vibe. Followed then by Gobo who I'm thinking was an only child. Most likely a little spoiled, he tends to get his way. And finally Moki. I love Moki she's kind of hard to figure out. A flower child yes, the oldest yes, possibly had one other sibling who is also a free spirit who goes with the flow.