Adding to what Smokefoot already said, I don't think the experience is the main factor; the set of skills change, you'll need to have deeper project management knowledge, communication abilities, etc.
Experience is important for two reasons: to be accepted as a leader by the others, and to be comfortable with the products and processes of your company. But this is a prereq, not the decision factor, which should be the former items.
And after a certain threshold experience has diminishing returns for such a position. When you move from developer to team leader you'll hardly do any coding anymore, nor you'll have time to inspect what other less experienced developers did, so if you accumulated a lot of technical experience it'll be wasted when you're in a management role. In such cases there should be a position for senior system architecht, for instance, that'd be a best fit. THAT is definitely a case in which the more experience, the better.
The measure to check such things is a difficult issue. Courses attended, standardized tests that HR of big companies and specialized consulting firms apply can help, but they won't give a definitive answer about if someone is prepared or not for a given job. Also certifications like PMI help, but don't solve 100% of the problem. One possible approach would be, if the company is big enough for that, to have each candidate temporarily as a team leader for a small project, and later collect and compare the results.