I hate to say it but how you look is important. Rubio did not look presidential in the least because he is young and looks young for his age.
I whole-heartedly disagree. Voters appreciate 'handsome', and younger candidates deliver that better. The major thing preventing tickets with younger candidates is the parties's insistence upon people whom they believe are 'more electable', whatever that means. Rubio would will have done well against the Democratic nominee in the GE.
P.S. This country needs another JFK.