Ahh now that I actually read more...it says you gain Leadership as a bonus feat. And at level 1 in the table for Leadership you don't get a cohort at that level. Mainly because the prereq is Character Level 7 for Leadership according to the PRD.
I think the text needs to add something like "You still must meet the prerequisites for the Leadership feat to gain followers."
Or give a new table for cohort level by character level.
Or give the "minimun level 1" addition you mentioned.
OR (and I like this best) add "Must be at least 3rd Tier before selecting this ability".
Well, after level 3, it's not really game breaking. First and 2nd level is a bit touchy, but the raw numbers of a co-hort don't cause a problem. And locking it to Tier 3 doesn't fix the issues unless Tier 3 now requires you be higher level.
Technically you can play a Level 1/Tier 3 game. Weird but legal.