Not "could hurt; "will" hurt. Younger people may be naturally inclined to the left because they still believe in "free stuff" and unicorns, but many are not so stupid that they cannot respond to a well-reasoned, inspiring, positive explanation of how the values of traditional liberty and free markets are the best means of advancing humanity. The problem is that almost no-one since Reagan has been able to, or wanted to, take that position. Instead, we've had a generation's worth of negativity from the GOP; that will, and has, turned off a lot of older people as well as turning off younger people. Donald Trump has simply upped the ante on the negativity, and that will further alienate people - both old as well as young - from the GOP. Squandered political capital is hard to rebuild; it will take the GOP a very long time, perhaps another generation, to rebuild the political capital Trump has so uselessly squandered.