The main problem with your reasoning is that while teens may represent 35% of the market, non-teens must represent close to 65% percent of the video game market.
If your company targets the 35% and mine targets the 65%, if we both pull in just ten percent of the people we target, I'll make twice as much money as you do, more or less.
My argument was merely to show that the teens have plenty of money, in general.
Now, add to the point from the WotC Market research: While the teens may not spend as much on the game per individual, it turns out that (at the time) 79% of people who played tabletop RPGs learned D&D between the ages of 12 and 18!
The older folks are only spending more after years of already being gamers - if you don't already have them, they are a poor choice to target them for sales. If you want to grow your long-term player pool, you need to get them while they are teens. Failing to target teens is a good way to doom your long-term business.