Rather than a retirement age, you could just appoint a judge for a fixed tenure. How long that is could be based on the current age of the appointee, or could be less to best avoid clusters of appointments. Tenure of course needs to be long, probably with a minimum in decades to cover multiple election cycles.
Indeed. This is also more future-proof. If people live longer and retire at say 120, do we really want judges to sit there for 80 years without a chance to re-evaluate them?