Weight of a person can be expressed as a function of their age. The function usually varies from person to person. Suppose this function is identical for two brothers, and it monotonically increases till the age of $50$ years and then it monotonically decreases. Let $a_{1}$ and $a_{2}$ (in years) denote the ages of the brothers and $a_{1} < a_{2}$
Which one of the following statements is correct about their age on the day when they attain the same weight?
- $a_{1} < a_2 < 50$
- $a_{1}<50 < a_2$
- $50 < a_1 < a_2$
- Either $a_{1}=50$ or $a_{2}=50$
