。
The elderly aren't always wiser than the young.
Literal
Old-people [subject-が] young-people [comparison-より] always wise [definitional-とは] not-necessarily.
~とは限らない ('it's not necessarily the case that') is a useful pattern for challenging assumptions. より marks the comparison. いつも + negative = 'not always.' A thought-provoking counterpoint to the cultural deference Japanese typically shows toward elders, expressed without harshness thanks to the hedging とは限らない.