I was looking at the TACP CFETP, and saw when that TACPs can join the 21st, 22nd, 23rd, and 24th STS(obviously with the right amount of experience, character, and mental fortitude). Can anyone clarify?

Yes, TACPs are based at Active Duty STS units to provide more JTACs for the STS mission set due to high demand for JTACs and a shortage of Combat Control JTACs. If CCT produces enough JTACs to fill the manning requirements, the TACPs will transfer back to TACP units. I don't know when/if this will happen.
The ANG is not doing this because the TACPs are an AFSC Substitution, meaning they are a temporary substitution until CCT manning is up to par. Our manning is fine and we don't want to hire a guy, then have to fire him when we get enough CCTs through the Pipeline. Active Duty doesn't have this concern because the TACP is filling a slot in the USAF and can just transfer to another unit. ANG units can't do that so easily as the guy would have to be discharged from one State and enlist in another and there is no guarantee any other State will have an opening. It simply wouldn't be fair to hire a guy knowing that you might have to fire him and not have a place for him to go.

Also, given current CCT manning (we have a waiting list for Trainees right now) we don't have a shortage of CCTs that the TACPs could fill.

Bottom Line, If you want to be in an STS unit go CCT.