how old is the Washington monument?

Answer 1

The National Park Service indicates that it was begun in 1848. They have a very nice document about it ... you might also want to look at the website for the monument.
http://www.nps.gov/archive/wamo/home.htm

Washington Monument - A History
TABLE OF CONTENTS
PREFACE
LIST OF ILLUSTRATIONS
I. HISTORICAL INTRODUCTION
Early Proposals
Organization of the Washington National Monument Society

II. CONSTRUCTION OF THE WASHINGTON MONUMENT, FIRST PHASE, 1848—54
The Foundations
Laying the Cornerstone
First Construction Phase, 1848—54

III. INTERIM PERIOD, 1855—76
Memorial Stones
Theft of the Pope's Stone
Seizure of the Monument
The Civil War

IV. CONSTRUCTION OF THE WASHINGTON MONUMENT, SECOND PHASE, 1876-84
Concurrent Resolution of July 5, 1878
The Army Investigation Boards
The "Story" and "Marsh" Plans
Stabilizing the Foundations

V. COMPLETION OF THE MONUMENT
Ironwork
Completion of the Shaft
The Pyramidion
Wages and Workmen
Setting the Capstone

VI. THE POST-DEDICATION PHASE, 1885—88
The Dedication of Completed Monument
Post-Dedication Construction
Inserting the Memorial Stones
Redesigning the Entrance Doors
Protection Against Lightning
Filling the Terrace Lodge
Operation of the Monument

VII. THE GROUNDS OF THE WASHINGTON MONUMENT AND COMMUNITY USE
The McMillan Plan and the Monument Grounds
Visitation and Maintenance
Publicity Incidents
Appropriations
Proposed Visitor Information Center
Elevator Safety
Community Use of the Monument

Answer 2

Tourists. There were tourists inside the Washington Monument. Lots of them standing close together in a small space. I got to practice my conversational Chinese with a group from Taipei. After that, it was closed down for years again, for some kind of renovation. Guess it's open again.

Answer 3

Forget how old it is...learn what stones compose it, and where they came from.

More interesting...find out the effect it has upon Washington DC, spiritually.