The term for this form of inheritance is ultimogeniture.    From Wordnik.com.  ['Born to Rebel'] Reference

Unlike primogeniture, ultimogeniture lays the responsibility for family continuity on the shoulders of the youngest, leaving the older ones to strike out on their own.    From Wordnik.com.  ['Born to Rebel'] Reference

Jefferson would have been just as much opposed to it if it had been ultimogeniture, since what he objected to was the accumulation of property, not the fact that it was the eldest son who took all.    From Wordnik.com.  [Growing Old: An Exchange] Reference