BUG: Sim won't age up

Problem
My sim doesn't age up. Either they celebrate forever, my Sim looks like a little person or they have all the characteristics of the last age group.

Cause 
unclear, might have something to do with cc skins or the lack of skins

Little Sims can be explained by the not-finished growing up process. The Sims have the skeleton of the the new but the clothing of the old age group what makes them look the way they do. It might be possible that wrongly categorized clothing also results in this problem.

Things you can try
Make sure that you don't have any non-default skins that were made before LN (October 2010). The sliders that were introduced with LN seem to lead to problems with those. Unfortunatly, non-default skins are getting packed with exported Sims. You will need to uninstall the Sim to get rid of the skin. Sims that appear pitch black in your game should be uninstalled as well.

For some, changing households helped aging the Sims up. Play with another family for a while.

To make a little Sim normal again, try changing his cloth.

Sims can be aged with the cheat testingcheatsenabled true, then shift-click to age him up. This does not always work, though.

Mods that help with the problem

• Der MasterController has an option to age your Sim that usually works

Further Reading

• BUG: Aging troubles
• Game Help:Sims 3 Aging