Explanation:

• 2 only
• Collegium for the appointment of high court judges includes the Chief Justice of India and four senior-most judges of the Supreme Court. (Incorrect - The Collegium system for the appointment of high court judges includes the Chief Justice of India and four senior-most judges of the Supreme Court, but it does not specify that only the senior most four judges are involved. The composition can include other judges as well.)
• The retirement age of Supreme Court judges is 65 years. (Correct - The retirement age of judges of the Supreme Court of India is 65 years.)
• So, the correct combination is "2 only," which corresponds to option 2.