While We're Young (2014)

Whenever someone does a movie about aging and tries to both get it right and to be funny, it is a fine line that is fraught with difficulty.  This movie has an excellent cast and it really does a good job of being occasionally very funny about a couple coming to grips with middle age. 
Josh (played by Ben Stiller) is a slightly obsessive, slightly narcissistic documentary film maker with almost no sense of humor about his work and less of one about aging.  When his doctor tells him he has arthritis in his knee he is so incredulous he thinks it is some other sort of thing that they are using that word to describe but it could not be degenerative joint disease.  His wife Cornelia (played by Naomi Watts) is a film producer and the daughter of a famous documentary filmmaker (played deftly by the wonderfully understated Charles Grodin). 
They are getting old, they were unable to have children, and their friends are having babies in their forties, which is of course exhausting them and making Josh and Cornelia feel left out.  Into that void step Jamie (played by Adam Driver) and his wife Darby (played by Amanda Siegfried--this movie has a great cast).  Jamie is an aspiring documentary film maker, and while the younger couple invigorates the older couple, you can see that it is not going to end well for Josh.  The ending is largely what you would expect it to be, but the dialogue is crisp and real and the whole thing is well worth watching, especially if you fall into Josh' demographic.