It is very probable that the sex ratio of shidduch age singles in frum circles is at least 105:100 male to female and the whole NASI theory holds NO water.
The national average in the USA at birth is 105:100 male to female, it does fall to about 104.3:100 by age 24 but that due to boys dying due to gang violence, drug overdose and other vices that be’h are not so prevent in our circles. Additionally the ratio among Caucasians is 106:100 and among Asians 107/8:100. African Americans have 103:100 ration and drag down the national ratio.
So it is almost certain that the age gap theory is NOT the cause of the shidduch crisis.