from apc's airline profile data -

w/b percentage -

UA 24%
DL 19%
AA 16% (AA approx. 17% next year)

Larger than 767 w/b percentage (ie 330/747/777/787) -

UA 17%
AA 12% (AA approx. 14% next year)
DL 7%


If UA's fleet average is 11 years, and the 747 fleet age averages 30 years, parking all the 747's would only drop the fleet average age by .6 of a year.

Using that assumption AA's younger fleet gap of 2.9 years would become 2.3 years.