Nielsen conducted a study of Android applications used by age groups. 18-24, 25-34, 35-44 based on usage going back 30 days from. What I find interesting is that all of the the most commonly used top 6 applications, with the exception of Facebook all belong to Google across all of these age groups.
Nielsen findings:

Nielsen analyzed usage data from its proprietary device meters on the smartphones of the thousands of consumer panelists who agreed to be part of Nielsen’s ongoing Smartphone Analytics research.
Staying Social
Facebook’s popular app is the most active among Android owners 18-24 and 25-34, who both hover at around an 80 percent active reach. Additionally, more than three quarters of users 35-44 used the app recently as well.

 

Google’s YouTube app gets heavy usage from Android smartphone owners 18 -24: 64 percent have used it in the past 30 days, compared to 56 percent and 51 percent of 25-34 and 35-44 year olds. A preference for media apps with a social dimension (e.g. Words with Friends) among the 18-24 set is also reinforced by their sizable usage of music and video apps (e.g. Pandora) compared to older demographics.

 

Play Time
Not just for the kids, the ubiquitous game, Angry Birds, appeals more to those 35-44 when compared to other age groups: 35 percent of them have used the app in the last 30 days, while only 22 percent of those 18-24 and 29 percent of 25-34 year-olds launched the game.

 

Apps and More for Sale
Apart from gaming, the 35-44 segment demonstrates a greater inclination to shop using the Amazon AppStore: 24 percent of them used the app in the last 30 days, while only 14 percent of those 18-24 did the same. Groupon appeals more to those 25-34, not even making the top 20 ranking for those 18-24. A similar trend was found on Google+: active reach was higher for those 25 and older when compared to the 18-24 demographic.

Source – Nielsen Wire.