Q 1: What's the meaning of
"'A man's got to TAKE IT WHERE HE FINDS IT,"
This means that a man has to take advantage of his opportunities, wherever he may find them. It is a cynical statement though, because it implies that those opportunities might not be moral or ethical.
"especially when he starts GETTING ALONG in years.'?
This means that he is getting older, and the implication is that he is starting to notice his age, so it might be that he is no longer feeling 'young', or perhaps he is middle aged, for example, and therefore needing to think about things like his health, his situation in life, etc.
Q 2: What's the meaning of 'parked at the end of some back road'?
In this context, Jack and Wendy are parked in their car at the end of the road.
Sometimes, we use "parked" to mean sat or "park" to sit, so you could say "park your self on that sofa". It's more slang to use it in that way, though.