input: Write a python function to create an SQLite database with a table for storing user information.
  assert create_database('test.db') == True
  assert os.path.exists('test.db') == True
output: import sqlite3
  import os
  
  def create_database(db_name):
      try:
          conn = sqlite3.connect(db_name)
          cursor = conn.cursor()
          cursor.execute('''
              CREATE TABLE IF NOT EXISTS users (
                  id INTEGER PRIMARY KEY AUTOINCREMENT,
                  name TEXT NOT NULL,
                  email TEXT UNIQUE NOT NULL,
                  age INTEGER
              )
          ''')
          conn.commit()
          conn.close()
          return True
      except Exception as e:
          return False