Subsetting a data frame with top-n rows for each group, and ordered by a variable

One solution using ddply() from plyr

require(plyr)
ddply(d1, "Gender", function(x) head(x[order(x$Age, decreasing = TRUE) , ], 2))

With data.table package

require(data.table)
dt1<-data.table(d1)# to speedup you can add setkey(dt1,Gender)
dt1[,.SD[order(Age,decreasing=TRUE)[1:2]],by=Gender]