Bobby Hill is still twelve, almost two years after his twelfth birthday, so it may be that he is destined to stay twelve or to age slowly. It seems to me that Joseph used to be drawn taller than Bobby, but is now about the same height, though still thinner. In one early episode Joseph's (twelfth or thirteenth?) birthday was a few weeks after Bobby's twelfth birthday (which is April 6th or 7th, according to _The Boy Ain't Right_ by "Hank Hill"), making Joseph slightly younger or almost a year older than Bobby. I didn't notice if Joseph was in the same room when Peggy was substitute teacher in Bobby's class.
In the deer-hunting episode, Luanne's hair is short again, with maybe a three-month growth (it being in real time about that long since she was rescued from the explosion). So there may be a question about whether the medium and long length of her hair in recent episodes indicates that she has accepted the idea of wearing a wig (which is unlikely in view of the difficulty she had in raising the money for beauty-school tuition) or whether there is just no significance to the placement of episodes (which may mean that they just skip around during the time Bobby is about twelve).
There are a couple of new data points in the wink-wink-nudge-nudge saga of John Redcorn. He again is shown with his shirt off when Dale Gribble arrives home, but this time he is in the presence of Bill Dauterive and Luanne Platter (in addition to Nancy Gribble) as he is putting the shirt on. My guess is that their presence lessens the significance of the shirt.
John Redcorn also gives Joseph a (used) knife before Joseph's first hunting trip, but he punches the word "father" more than the word "my", which reduces (to my ears) the significance of the "obvious" generational hint, and keeps the "facts" consistent with the possibility that Joseph is the son of Dale and his first wife (perhaps John Redcorn's sister, who may have died in childbirth). There are of course conflicting hints with Nancy's question about when "exactly" Dale would be returning and Nancy's parting statement to Dale about her boy's first hunt. But there are supporting hints in Joseph's new-found aptitude for conspiracy theories ("The Gribble doesn't fall far from the tree").
There were some editing glitches involving the timing of the placement of the heart on the practice deer and the timing of the truck clean-up, which suggest to me that there is a fair amount of shifting around done after the animation, and that little weight should be given to hints that involve sequence of events.
I got the impression from early episodes that Hank Hill is 39 or 40 years old and had been married to Peggy (who in turn didn't get her first kiss from a boy until she was twenty (and she said he's dead now)) for about twenty years. Hank and the guys appeared to be about the same age in the Order of the Straight Arrow episode and in the first-hunt "photograph" on Dale's wall in the deer-hunting episode, but in that same episode Dale said that his first hunt (presumably at the customary age of twelve) was twenty-five years ago.
Bobby also shows a keen sense of right and wrong and does a great death scene in this episode.