[1] He served as Sun's vice president and chief researcher and director of the Science Office,[2] until leaving on June 9, 2008, to join Kleiner Perkins Caufield & Byers as a partner to work on green technologies for global warming; he departed KPCB in 2010 to apply what he had learned "to broader issues in other parts of the world".

[3][4][5] In 2006, he joined the board of the Tegla Loroupe Peace Foundation, to build a school and orphanage in Kapenguria, in remote north-west Kenya.

Gage received his bachelor's degree in 1975 from the College of Natural Resources at the University of California, Berkeley.

[10] In June 2008, Gage retired from Sun Microsystems and joined Kleiner Perkins as a venture capitalist along with Al Gore.

He has served on the boards of the US National Library of Medicine, of FermiLab, the Berkeley Mathematical Sciences Research Institute, and other scientific and educational groups.

His father was James Robert Gage, born in Woodville, East Texas, and president of the UCLA Class of 1935, captain in the United States Navy, and senior manager for Douglas Aircraft in Long Beach, then for McDonnell Douglas Aerospace in Seal Beach.

He worked on the Robert Scheer for Congress campaign in 1966, almost defeating a Democratic congressman who supported the war.

In the 1976 Jimmy Carter campaign, he helped train staff, and organized the final rallies in California.

In the 1980 Ted Kennedy campaign, he was assistant national press secretary and trip director, and member of the traveling party.

In 1969, Gage was asked by Bill Hanley, the owner of Hanley Sound, the staging and sound system used at Woodstock, and the system Gage used in Washington, D.C. for the Vietnam Moratorium, to come to Palm Beach, Florida, to take over producing the International Palm Beach Music and Art Festival.

King, Janis Joplin, the Rolling Stones, Sly and the Family Stone, Jefferson Airplane, the Byrds, Sha-Na-Na, Country Joe and the Fish, Steppenwolf, Johnny Winter, Sweetwater and twenty other groups performed;[14] there had been strong opposition from the Governor of Florida, local law enforcement, and some local churches.

Subsequently, Gage was called to rescue the Louisiana Celebration of Life Festival after two people had drowned;[15] produced the New York Shea Stadium Festival for Peace Concert with Peter Yarrow, Janis Joplin, Creedence Clearwater Revival, Herbie Hancock, Miles Davis, Dionne Warwick, Paul Simon, Sha-Na-Na, Johnny Winter, and fifteen more,[16] the Philadelphia Peace Concert, and several other events involving over 100,000 people.

In 1982, Gage joined Bill Joy, Andy Bechtolsheim, Vinod Khosla, Scott McNealy and others to found Sun Microsystems.

For the World Economic Forum, he helped organize the Jordan Network Initiative with John Chambers of Cisco and Eric Schmidt of Google.

In 2000, Gage spent a year at the Harvard Kennedy School of Public Policy as a Shorenstein Fellow.

[21] Gage joined Connie Nielsen and David Warner in 2012 to build a large community center in Kibera, Nairobi, Kenya.

[22] The Kibera Town Centre[23] borehole can provide over 400 cubic meters of pure water a day to the 1,000 square-meter facility, which serves over 1,000+ people a day with a combination of educational and career services, showers, toilets, laundry, cafe, and financial services, and provides educational materials to the 4,000 students of neighboring Olympic Primary School, Kenya's largest primary school.

The facility is connected to high-speed fiber optic cable, and has built a half-gigabit wireless network for Kibera.

Gage did more than fifty satellite television programs on technology that were broadcast worldwide from Moscow, Rio, Mexico City, Beijing, Zurich, Mauna Kea, Berlin, Santiago, Kuala Lumpur, Cape Town, San Francisco, Paris, London, and other cities.