Hi.... Men grow height-wise until ~21 years old, although depending on the person they may experience slight changes until 25. For someone in their later twenties, you're already not producing the regul ar pulsatile bursts of growth hormone needed to stimulate longitudinal growth, but even if an exogenous source was provided, the growth region of the bone known as the epiphyseal plate has already shut down, so you'd only grow laterally.