A histogram displays the average body mass index of individuals across different ages, using data loaded from a CSV file via `d3.csv`. The visualization uses `d3.bin` to group ages into bins and `d3.scaleLinear` for both x and y axes, rendered as SVG rectangles with green fills. Customized axes are created with `d3.axisBottom` and `d3.axisLeft`, and the chart includes titled axis labels for age and average BMI. The example demonstrates ES6 module imports from the D3 v4 library.