Well, PCs get to advance as they face challenges and defeat their enemies - what about Hirelings?
Mircolite20's advancement system relies on the average level of your group - but Hirelings can make you somewhat more effective than would be expected. Torchbearers and Sages might not really assisst too much, but having a cadre of ten Men-at-Arms could really throw those numbers out.
If the players are using loads of Hencemen, consider not levelling any of them up - they're working as a large group of "mooks", and probably won't be learning anything they don't already know. But, if they only hire 1 Man-at-Arms, and he survives to the point that the players level up, consider adding a level of Fighter to the stat-block provided. If that seems a little too generous, maybe add +1 to-hit and +1 to one skill. Similarly, for other Hirelings, make them just a little bit better at what they do - a +1 here or there can show some advancement, while not allowing them to overshadow the players. As Sages don't come along with the party, I wouldn't go about leveling them up - unless the players bring them tomes of arcane lore, or something similar. Then, sure, give them a little +1 or +2, maybe even just to specific areas of research, to let the players feel a little bit more of a part of the setting as well as the game. Then, you open up more adventures, to find more books, and before you know it, the PCs are choosing to go raiding the lair of an Elder Dragon, just so their friendly local Sage can get himself a +1 t his Knowledge (Basket Weaving) skill... the game writes itself!
Or, you could take it as a "story-based" thing - say the PCs have three henchmen - a young torchbearer, a scribe, and a warrior. Which one do they seem to like the best?
Maybe the scribe takes maps, and has little other interaction with the group, and the warrior is pretty much a nameless meatshield for the party - they're not going to get a level-up. But maybe the young torchbearer saved the Fighter's life, and he wants to take him on as a squire. That warrants a level of Fighter, in my book, especially if the players are already a few levels above 1st. It helps that character to be more effective, and also allows the players to keep around a favoured NPC.
Just do what seems cool and appropriate to the character and the story, and you should be fine!