Older people and babies go to the back of the line

Because either too much money or not enough has already been invested in those age brackets. Read about it here at the WSJ:

Dr. Emanuel concedes that his plan appears to discriminate against older people, but he explains: "Unlike allocation by sex or race, allocation by age is not invidious discrimination. . . . Treating 65 year olds differently because of stereotypes or falsehoods would be ageist; treating them differently because they have already had more life-years is not."

The youngest are also put at the back of the line: "Adolescents have received substantial education and parental care, investments that will be wasted without a complete life. Infants, by contrast, have not yet received these investments. . . . As the legal philosopher Ronald Dworkin argues, 'It is terrible when an infant dies, but worse, most people think, when a three-year-old dies and worse still when an adolescent does,' this argument is supported by empirical surveys." (thelancet.com, Jan. 31, 2009).