Expression #1 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'mikomo1_movies.roles.id' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by
SELECT *, DATEDIFF(NOW(), birth)/365 AS age, COUNT(DISTINCT roles.movie) AS movie_count FROM roles, people WHERE roles.person = people.id AND people.death = '0000-00-00' AND EXTRACT(YEAR FROM birth) != '0000' GROUP BY roles.person HAVING COUNT(DISTINCT roles.movie) >= 1 ORDER BY age DESC LIMIT 100
ActorBornCurrent age