input: Write a python function to greet users based on their age.
  assert greet_user("Alice", 17) == "Hello, Alice, welcome to our website."
  assert greet_user("Bob", 30) == "Greetings, Bob, how can we help you today?"
  assert greet_user("Charlie", 65) == "Welcome, Charlie, thanks for visiting us."
output: def greet_user(name, age):
      if age < 18:
          return f"Hello, {name}, welcome to our website."
      elif age < 60:
          return f"Greetings, {name}, how can we help you today?"
      else:
          return f"Welcome, {name}, thanks for visiting us."