No different to the average age of those who sat in the upper west and upper east at the Dell. I imagine the average age of fans in the Northam equals things out (I won't start on average IQ...) The only time it should be cheap tickets for kids is for cup games. In fact, it has been cheap for them, yet they (parents allowing) havn't turned up, so I'd say the market is not there.
Noticed that Anfield is looking to develop to 60,000 seater at cost of £159 million. Not suggesting that an extension to SMS that large is even being mooted, but the possible cost of an extension at Saints would suggest it's not happening any time soon.