You don't need to stat any inane followers. You don't need to stat followers that's main purpose is using a spell, such as casting mount for transportation, or light, or what have you. If you want to call upon their save DCs, ability scores, skills or feats, you need to stat them. Feel free to be reductive to their vocation. Practically speaking it's fine for them to identical stats, even though they may have some nuance. You can also put footnotes for followers that subsect the above stats (that you provide) to show some nuance. An example would be scribes. You might assign knowledge (varies) and put how many have each knowledge in footnotes. Further more you might put that they range in age, from those that had idle periods of wasting or maybe had to raised from the dead so much, they are only low level, despite being <age bracket>. Try to observe this is not to be abused. Most followers, of any class, should follow an age by race current age. I don't mind some caveats for devoted followers that are older; like I said they may have been raised from the dead a bunch, or had idle periods.