Weight of a person can be expressed as a function of their age. This function usually varies from person to person. Suppose this function is identical for two brothers and is monotonically increasing until the age of 50 years, after which it monotonically decreases. Let \( a_1 \) and \( a_2 \) (in years) denote the ages of the brothers, where \( a_1 < a_2 \).
Which one of the following statements is correct about their ages on the day they attain the same weight?