Question: Calculate the average age of patients with prediabetes care plan.
SQL: SELECT CAST(SUM(CASE WHEN T1.deathdate IS NULL THEN strftime('%Y', T2.STOP) - strftime('%Y', T1.birthdate) ELSE strftime('%Y', T1.deathdate) - strftime('%Y', T1.birthdate) END) AS REAL) / COUNT(DISTINCT T1.patient) FROM patients AS T1 INNER JOIN careplans AS T2 ON T1.patient = T2.PATIENT WHERE T2.REASONDESCRIPTION = 'Prediabetes'