A recent report from HSBC, sent to the bank's clients, says that on average people will see their highest productivity growth when they're young, with increases in middle age dwarfed by those made in our 20s and early 30s, according to Slate. Defining productivity as contribution to the economy in terms of output, it shows that growth spikes in early adulthood, then slowly increases until around 50, at which point it gradually declines until retirement, at which point it plummets completely. Slate notes that this matches well with other research that shows most income growth happens between 25 and 35, at which point increases become much less dramatic.