Stanford Medicine Jul 10 2025 The candles on your birthday cake don't tell the whole story. As anyone who ever attended a high-school reunion can tell you, some people age faster than others. Whoever put the candles on your cake probably didn't have to guess your chronological age. But research has shown that we also have what's called a "biological age," a cryptic but more accurate measure of our physiological condition and likelihood of developing aging-associated disorders from heart trouble