bfb3a285_SSA_Handbook___211__If_the_worker___
A worker disabled before age 31 who does not have sufficient credits to meet 20/40 requirement. Note: Special insured status may apply to a worker who becomes disabled after age 31, provided the individual had a period of disability prior to age 31. See §208. [If the worker...] 
Has credits in one-half of the quarters elapsing in the period after the quarter of reaching age 21 and up to and including the quarter of becoming disabled. The worker needs at least six credits (see §208); or if disabled in a quarter before turning 24, he or she needs six credits in the 12 calendar-quarter period, including the quarter in which the disability began and immediately before becoming disabled.
SSA Handbook § 211
If the worker...