This isn't just the result of people tending to become more conservative as they get older and of older people being less likely to be plugged into the internet. The pattern holds consistently across age ranges. Among those under 30:
Adults aged 30-64:
Seniors, aged 65 and older:
The "silent majority" remains a fairly relevant phrase today.
Parenthetically, self-described liberals and conservatives are about at parity when it comes to intelligence. Moderates tend to be of more modest intellectual capabilities, so the fact that they are less likely to broadcast their political sentiments than the more politically committed isn't surprising since many of them probably don't have established views and among those who do have them, many haven't given much thought to them.
GSS variables used: POLINTER(1-2)(3-4), AGE(18-29)(30-64)(65-89), POLVIEWS(1-3)(4)(5-7)