This is a very good and tricky question to answer. In my field, ranking doesn't really matter unless the school is one of the top 5.
If this is the case in your field too, then you would use ranking to help you make a decision if everything else is very similar (in my field, advisor's reputation and research topic is way important). I imagine that highly ranked schools have very reputable faculty too, but in a PhD, the specificity of a topic plays a higher rule. Not all too five schools have resources/faculty to study/test topic X. For instance, in civil engineering, UC Berkley is one of the prestigious school and always have a 1-5 ranking at any given year. It very famous for earthquake engineering, however if you would like to study something like structural fire engineering (keep in mind both earthquake and structural fire eng. are sub fields of civil engineering), you are better off going to a school ranked way below Berkley (or even to a Canadian/European school)!
As for the faculty, I'm not sure if some departments have more "young" faculty as oppose to older faculty. I have worked with both and can assure you that it is highly dependent on the faculty member persona. Age of a faculty doesn't or shouldn't be a very important criterion. If you are thinking in the line of being active, have unique ideas and stuff like that and you are worried that being with an older faculty member would mean that you will be working with an old school arrogant guy who you will meet once a month and publish minimum number of papers, then fear not!
You will be surprised of how many young professors who get their PhD and think that they know everything. Also, you will be equally surprised of how many well established professors who think anything new (for instance, FE simulation) is a type of a gaming platform.
The key is to choose an active faculty with high reputation and who is easy to work with. Do your research and ask graduate students. They should have better insight and can provide with behind the scene information.
One more thing, good professors will always be on top of their research, aware of the up-to-date technology and current research regardless of their age. It is true that well established faculty might have better connection and funding. This is due to how long they have been around and their natural progression. It is also true that younger professors might have a better grasp at newer technologies. But keep in mind that those young professors that might have graduated in the last few years most likely had an "older" advisor.