This is only an A level suggestion, but what we did once was show particpants a picture of a woman or man and ask them to write down how old they thought he/she was, on a piece of paper. One group are shown a picture and write on a blank piece of paper, and the other group is given a piece of paper with 'other participants' suggestions. Supposedly, those with a higher level of conformity write an age similar to what is on the rest of the page.
Hope this helps in some way!