Developer to team leader [duplicate]

Question

This question already has an answer here:

• How does one become a leader in a team of programmers? [duplicate] 5 answers

How much experience is considered enough for a developer to become a team leader?

For IT managment what is the measure to check if the current team member is good enough to become a team leader (technical level, interpersonal level)

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updated: removed second part of the question for being duplicate (see comments)