This bar chart displays the average percent change between first and second half marathon times across age groups for the 2024 Boston Marathon, with the y-axis fixed from 0% to 25%. The visualization groups runners by age category and computes the mean percentage slowdown per group. Built with React and D3 v7, it uses d3.csv to load the data, d3.scaleBand for the categorical x-axis, d3.scaleLinear for the y-axis, and d3.mean to aggregate the values. Bars are rendered as SVG rectangles filled with steelblue.