At fifty counsel

… בן חמישים לעצה …
וּמִבֶּן֙ חֲמִשִּׁ֣ים שָׁנָ֔ה יָשׁ֖וּב מִצְּבָ֣א הָעֲבֹדָ֑ה וְלֹ֥א יַעֲבֹ֖ד עֽוֹד׃

- במדבר ח:כה

Pirkei Avot Chapter 5.
"He [Yehuda ben Taima] used to say: At five [one should begin the study of] Scriptures; at ten, Mishna; at thirteen [one becomes obligated in] the commandments; at fifteen [the study of] Talmud; at eighteen the wedding canopy; at twenty to pursue; at thirty strength; at forty understanding; at fifty counsel; at sixty old age; at seventy fullness of years; at eighty spiritual strength; at ninety bending over; at one hundred it is as if he has died and passed on from the world."

BBC has an article titled Happy Birthday, Mr President in which advice columnist Amy Dickinson counsels the President on achieving the milestone of reaching 50.
"If President Obama asked me for advice on this mid-life milestone (he told me once that he reads my column), I'd point out that at 50, when you start every day by seeing your parents stare back at you in the bathroom mirror, the real gift is that you're forced to reckon with the unavoidable, inescapable truth - that the luckiest of us will escape middle age into old age.
The idea is to do the least amount of damage while we get there."

Read full article: http://www.bbc.co.uk/news/14398036