title: Add multiple labels on ggplot2 boxplot
body: <p>I am trying to add labels with the mean age of the males and females on this boxplot for 2 groups. So far I was only able to do it by group but not by gender and group. </p>
  
  <p>My data frame: </p>
  
  <pre><code>Age=c(60, 62, 22, 24, 21, 23) 
  Sex=c("f", "m", "f","f","f","m")
  Group=c("Old", "Old", "Young", "Young", "Young", "Young")
  
  aging&lt;-data.frame(Age, Sex, Group)
  </code></pre>
  
  <p>And the command for the plot:  </p>
  
  <pre><code>ggplot(data=aging, aes(x=Group, y=Age))+geom_boxplot(aes(fill=Sex))
  +geom_text(data =aggregate(Age~Group,aging, mean), 
  aes(label =round(Age,1), y = Age + 3), size=6)
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/tFqlg.png" alt="Graph with 2 groups and 2 genders per group"></p>