Some redwoods are at least 1,000 years old. The oldest known Giant Sequoia based on ring count is 3,500 years old. Most mature trees are 500 to 800 years old.

Conifer (Coniferales ) Order
Cypress  (Cupressaceae) Family
   Giant Sequoia  (Sequoiadendron) Genus 
     Giant Sequoia (Sequoiadendron Giganteum) Species
   Redwood (Sequoia) Genus
      Redwood (Sequoia Sempervirens) Species

The bald cypress (Taxodium distichum) and dawn redwood (Metasequoia glyptostroboides) are closely related to Sequoia.

Sequoiadendron Giganteum (Big Trees, Giant Sequoia)
Up to 30 ft diameter and 270 ft tall and 3,500 yrs old (General Sherman in Sequoia National Park.)
Habitat: Elevation 4,000-8,000 ft. west side of the Sierra Nevada Mountains.
32 scattered groves from Placer to Tulare Counties.
Kings Canyon and Sequoia National Parks (NP)
Calaveras Big tree State Park north of Sonora.

Sequoia Sempervirens (Coast Redwoods)
Up to 16 ft in diameter and 350 ft tall.
Typically 8 - 10 ft in diameter and 200 - 275 ft tall.
In 2006 a redwood in Redwood National Park near Crescent City in Northern California was measured at 379.1 feet tall, the worlds tallest living thing.
Habitat: Pacific Coast.
Big Basin Redwoods State park (North of Santa Cruz), Muir Woods National Monument, Redwood Natl. Park (near Crescent City), Humbolt Redwoods State Park, Julia Pfeiffer Burns State Park (Big Sur)

Japanese Cedars (Cryptomeria japonica), introduced into the US, has foliage resembling the Giant Sequoia.

Incense Cedar (Libocedrus decurrens) has bark similar to Sequoias.
They grow up to 125 ft with a diameter up to 7 ft.

Books:
Trees of North America, by Brockmanand Merrilees

Links:
Seeking out the largest living things on earth at Orion magazine