The Sony/Microsoft systems don't have a specific age group, rather, an interest group.
Today, most of America and Japan are online, meaning that internet (specifically Broadband) use is now quite mainstream, thus appealing to younglings checking out Nick.com to grandparents looking at pictures of their Grandchildren on Flickr. That is why all three next-gen systems are online compatible out of the box, the Wii being even more flexbile than the 360 given to its built in WiFi antenna. Also of interest is that the Wii and PS3 both feature online browsers out of the box for no additional cost (Opera for Wii will not be included after June 2007)
So, what market is each company going after, then?
It's clear that Microsoft is appealing to the male demographic ages 12 - 36. The dominant genre on the system is the shooter, followed by sports titles. While some may consider this a "mature" audience, get on Xbox Live and listen. What you'll hear is the high pitched ramblings of preteens There's nothing mature about the 360, just a desensitized youth.
The PS3 seems to be isolating its audience all together. It's no secret that Sony owes most of its last gen success to Grand Theft Auto and Madden. The Sony target group is likewise male, but is more in the range of 17 - 36. Now, with the higher pricetag, I estimate that the two ends of that spectru are going to be alienated, resulting in sales in the male demographic age 22 - 32, the reason being that there is more loose change in these pockets combined with a desire to play games still. I don't believe BluRay will draw people outside of this age group to the console.
As far as the Wii, the scheme is different. I estimate the target sales audience of the Wii to be in the range of 10 - 65. Yes, that large. Also, factor more women into the mix, broadening the number of sales possible. With its lower $250 price tag and inclusion of Wii Sports, the Wii si prepared to target people who never have purchased a console before. While great grandma might not be playing, I think that your old man might consider taking up the remote for a few rounds of Wii Sports and Brain Age. By targeting the young group with cartoony games and the older market with quick, fun, sensible games, the Wii also embraces the middle-aged group. Young married males will be wooed towards the system if their wives enjoy it, and games like Red Steel are attractive towards the "mature" audience of the PS3 and 360. The pricepoint doesn't hurt either.