How to get the first row of each group of a DataFrame?

How do I get the first row from each group of a grouped DataFrame?

Say, I want to find the sex and height of the tallest person in each age-group:

using DataFrames
df = DataFrame(sex = repeat(["F","M"], inner=4, outer=2), age = repeat(14:2:20,outer=4), height=100 .+100 .*rand(16))
16×3 DataFrame
│ Row │ sex    │ age   │ height  │
│     │ String │ Int64 │ Float64 │
├─────┼────────┼───────┼─────────┤
│ 1   │ F      │ 14    │ 127.878 │
│ 2   │ F      │ 16    │ 133.063 │
│ 3   │ F      │ 18    │ 186.6   │
│ 4   │ F      │ 20    │ 133.589 │
│ 5   │ M      │ 14    │ 186.655 │
│ 6   │ M      │ 16    │ 144.436 │
│ 7   │ M      │ 18    │ 155.293 │
│ 8   │ M      │ 20    │ 181.719 │
│ 9   │ F      │ 14    │ 199.308 │
│ 10  │ F      │ 16    │ 114.783 │
│ 11  │ F      │ 18    │ 111.551 │
│ 12  │ F      │ 20    │ 121.64  │
│ 13  │ M      │ 14    │ 177.85  │
│ 14  │ M      │ 16    │ 170.868 │
│ 15  │ M      │ 18    │ 126.169 │
│ 16  │ M      │ 20    │ 125.229 │

I tried this:

sort!(df, :height, rev=true)
first(groupby(df, :age))
4×3 SubDataFrame
│ Row │ sex    │ age   │ height  │
│     │ String │ Int64 │ Float64 │
├─────┼────────┼───────┼─────────┤
│ 1   │ F      │ 14    │ 199.308 │
│ 2   │ M      │ 14    │ 186.655 │
│ 3   │ M      │ 14    │ 177.85  │
│ 4   │ F      │ 14    │ 127.878 │

But this gives me the first group, not the first row from each group.

Then my instinct would be to "dot the first", but then I get:

first.(groupby(df, :age))
ERROR: ArgumentError: broadcasting over `GroupedDataFrame`s is reserved

In R I would do:

df <- data.frame(sex = rep(c("F","M"),2, each =4), age=rep(seq(14,20,2),4), height = 100 + 100*runif(16))
df <- plyr::arrange(df, plyr::desc(height))
plyr::ddply(df, ~ age, head, 1)
  sex age   height
1   M  14 193.4705
2   F  16 199.1906
3   M  18 165.1674
4   F  20 177.7445

What is the idiomatic way in DataFrames?

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