！！
Don't just wither with age — ripen with it!
Literal
Age-decline do-not! Age-mature do!
A wordplay-driven command contrasting two ways of aging: 老衰する (ろうすいする, 'to decline/deteriorate with age') vs. 老成する (ろうせいする, 'to mature/ripen with age'). Both share 老 ('old') but diverge: 衰 ('decline') vs. 成 ('accomplish'). するな is the prohibitive imperative; せよ is the classical/literary imperative of する, adding gravitas. The exclamation marks drive the motivational tone home.