The good news is that Fresh Expressions among young people are already taking place. I visited one such FE last night!
The challenging news is that we need more such FEs ... and we need to continually think about the form these FEs will take as time goes by (and the young people become middle-aged, then simply aged ...).
Back to last night: a particular feature of that Fresh Expression is its 'total youth' approach: young people lead, preach, plan the FE.
That is not the only way but it is something to think about. For example, do "oldies" (such as me at 50) get in the way of youth Fresh Expressions being Fresh?