IIRC, my dad mentioned that for a few years they had that option, AF lifer, 32 years.

I'll ask him tonight.

Yes, all retirees can, up to age .A retiree who is not yet 60 years old, or is disabled, will end up in Category 1 or 2. These members are eligible for call up in the event of national emergency or war. Which category they are assigned depends on their physical condition and how critical their skill is.

Disabled vets and those over 60 are not free of possible call up. Although placed in Category 3, they are evaluated on a case-by-case basis for recall in during a full mobilization.

Yes, retired means that until your are too old or infirmed to return to duty you can be recalled.  If you accept the pension, you have accepted a retainer.  Regular commisioned officers have a little different set of rules but they can be recalled to duty anytime they are needed.

Didn't this happen during WWII?

Yes, from O-6 (COL in AF, USA and USMC or CPT in USN) up, they can be called back.  O-5s sometimes can get back in.  

I thought they faded away.

Yes, retired officers are recallable for life.  Both Gen Macarthur and the current CoS of the Army are just a few examples of retired recall officers.

Quoted: I thought they faded away.

Nope, my dad was a full bird Colonel. He retired after fighting in WW2 and serving 37 years. During Desert Storm, he could have been called, just like me.

I know of 2 cases in the last 20 years

1st was the Commander of either US Army South, or Just Cause cant remember which was asked to come back on AD for that Operation.

2d was a former CINCSOCOM who is now I do beleive the Army COS, Dutch name Shoemaker in translation, but Im not even going to try and spell it right.

Yes, but it would be/has been very rare.

Yes.

In fact, any retired officer may be ordered to active duty under 10 U.S.C. 688.

See:  http://www4.law.cornell.edu/uscode/html/uscode10/usc_sec_10_00000688----000-.html

§ 688. Retired members: authority to order to active duty; duties
Release date: 2005-07-12

(a) Authority.— Under regulations prescribed by the Secretary of Defense, a member described in subsection (b) may be ordered to active duty by the Secretary of the military department concerned at any time.
(b) Covered Members.— Except as provided in subsection (d), subsection (a) applies to the following members of the armed forces:
(1) A retired member of the Regular Army, Regular Navy, Regular Air Force, or Regular Marine Corps.
(2) A member of the Retired Reserve who was retired under section 1293, 3911, 3914, 6323, 8911, or 8914 of this title.
(3) A member of the Fleet Reserve or Fleet Marine Corps Reserve.
(c) Duties of Member Ordered to Active Duty.— The Secretary concerned may, to the extent consistent with other provisions of law, assign a member ordered to active duty under this section to such duties as the Secretary considers necessary in the interests of national defense.
(d) Exclusion of Officers Retired on Selective Early Retirement Basis.— The following officers may not be ordered to active duty under this section:
(1) An officer who retired under section 638 of this title.
(2) An officer who—
(A) after having been notified that the officer was to be considered for early retirement under section 638 of this title by a board convened under section 611 (b) of this title and before being considered by that board, requested retirement under section 3911, 6323, or 8911 of this title; and
(B) was retired pursuant to that request.
(e) Limitation of Period of Recall Service.—
(1) A member ordered to active duty under subsection (a) may not serve on active duty pursuant to orders under that subsection for more than 12 months within the 24 months following the first day of the active duty to which ordered under that subsection.
(2) Paragraph (1) does not apply to the following officers:
(A) A chaplain who is assigned to duty as a chaplain for the period of active duty to which ordered.
(B) A health care professional (as characterized by the Secretary concerned) who is assigned to duty as a health care professional for the period of active duty to which ordered.
(C) An officer assigned to duty with the American Battle Monuments Commission for the period of active duty to which ordered.
(D) An officer who is assigned to duty as a defense attache or service attache for the period of active duty to which ordered.
(f) Waiver for Periods of War or National Emergency.— Subsections (d) and (e) do not apply in time of war or of national emergency declared by Congress or the President.