How does Median Age matter when picking a location?

[Hannah Thomas-Cunniff]

I'm a novice investor who is researching areas in Pennsylvania to invest.  My basic requirements to look for are:

• Population Growth
• Solid industries in place and economic growth
• Median housing prices are more than what a renter could typically afford
• Decent schools (Class B)
• Not a war zone (Class B)

Obviously, I'm looking for the golden nugget... and wherever I find it, do you heavily consider Median Age of the population? Are there any red flags if the population is either very young or very old?