My grandmother started walking five miles a day when she was sixty. She's ninety-seven now, and we don't know where the hell she is.
Speaking of grandparents that take a long walk to a far off place...
On his deathbed, having made the long trek to Egypt from Canaan, Jacob asks for Joseph and his kids, Efrayim and Menashe to visit. He blesses the two of them, raising these two grandchildren to the stature of tribes, of his own children and, in a tradition that stretches back to Cain and Abel, gives preference to the younger brother over the elder while implicitly doubling his favorite almost-youngest son’s portion. In effect, he enshrines the granting of the gift of primogeniture to his favorite son, giving the double portion normally reserved for the eldest to Joseph.
In blessing them, he stipulates that all his descendants should bless their sons 'as Efrayim and Menashe.' Traditional commentators have focused on two explanations for why this blessing was instituted by our ancient patriarch and has lasted to this day: family dynamics and tribal loyalty.
According to tradition, this is the first sibling preferential treatment which results in neither the arrogance of the victor nor the jealousy of the loser. Whereas on the tribal plane, these were the first two of Jacob's progeny to be born and raised outside the promised land and still maintain their loyalty to the emerging tribe.
I'd like to add the observation that raising kids is hard. Grandkids are generally easier, I'm told, because many of the disciplinary requirements are often unnecessary, left to the parents. As Sam Levenson said, The reason grandchildren and grandparents get along so well is that they have a common enemy.
The blessing allows parents to express their love for their sons, while disciplining them as necessary, as unconditionally as though they were grandchildren. Perhaps, if the boundaries are not too often broached, it's a way of parents allowing themselves to be Grandparents for a Day, once a week, on Shabbat.