Common Birth Dates asked for the expected number of pairs of common birth dates for a cohort of 1000 people whose ages were clustered around a certain value.

Now consider a similar question to the traditional birthday problem: If you attend a concert or other event where people tend to be of a similar age, how large would such an event need to be in terms of number of attendees, so that you'd have at least a 50% probability that there would be at least two people born on the exact same day (year, month and day)?

Again to make things specific: assume the standard deviation about whatever the mean age to be is 12 years and it follows a normal distribution.

Again feel free to vary the assumptions about the distribution.