Do you know this famous quotation? I love it because I've lived it.
He who is not a Socialist at 19, has no heart. He who is still a Socialist at 30, has no brain.
It is variously attributed to Winston Churchill, Otto von Bismarck, Woodrow Wilson, George Bernard Shaw, Georges Clemenceau, and Aristide Briand. The earliest citation I can find for it is François Guisot (1787-1874). So many people have observed the wisdom in this statement, and endorsed or borrowed it, that the statement has become axiomatic.
Certainly the young are Democrats. Is that any reason to expect these same individuals to still be Democrats 10-15 years from now? Of course not; there is every reason to expect them to mature into conservatives, as so many of us have done.