You should look for someone with relevant experience and relevant connections. Sometimes with age comes experience and connections but not necessarily.
Don't team up with an older co-founder if he(she) is just going to be window dressing.
"Young" people often handle the technology side. That's all nice, but if you're planing to run a business, being technically proficient isn't enough. You have to have someone who can handle the business side of things which includes in the very early days - how to get traffic over, marketing etc. the CFO comes at a much much later phase...
Technological youngsters often needs business mentors. Even Mark Zuckerberg of Facebook had that guy from Napster who helped him convert from a kid with a neat idea to a serious company by introducing him to VC's who would otherwise not even speak to him.
You may want to look into advisors and mentors. They are part-time, often senior (in the corporate sense) people who will give you advice. They act as wise people. You don't have to listen to them all the time, unlike co-founders.
I just attended the Web Expo 2.0 in San Francisco and I was struck by something. About 80% of the vendors were companies of all young (<30) people. The other 20% seemed to be all >45 people. (I refuse to call them "old". ;-) The 20% had products and services with depth and the obvious benefits of experience. The 80% had products and services that were fresh and innovative. Yet both groups seemed to lack what the other had. I wanted to take some folks by the hand, walk them to the next booth and say, "Look, you need what they have. Talk to these people." I didn't see one company that was a mix of ages. That is a true loss. I am in the 20% group but my crew is mostly 20-somethings. I can't imagine it any other way. Young people with brains (and that rare valuable quality, humility) recognize they have limited experience. Old people (there, I said it) with experience know they need young people with brains, energy, optimism, and ambition. Find yourself an older cofounder who appreciates that and you will be on your way.
Age alone doesn't qualify or disqualify anyone - risk tolerance is one factor to note. The person with two kids, a mortgage and all that over their head may not be able to put in the time commitment that some founding roles require. All the equity in the world will not pay their bills in actual cash.
You won't have all the skills to build a company on your own. Hopefully, you'll contribute the vision for the product and the tenacity and belief to get it made, and get it in customers' hands. To get the skills you need which you can't pay for outright, consider an advisory board role, and give out some small portion of ownership based on the contributions, for example.
You can't afford dead weight or window dressing in a founder role, young or old.