Database: legislator
Question: Based on the number of current legislators, calculate the percentage of legislators that served in 21st-Century.
SQL: SELECT CAST(SUM(CASE WHEN strftime('%Y', T2.start) BETWEEN '2000' AND '2017' THEN 1 ELSE 0 END) AS REAL) * 100 / COUNT(T1.bioguide_id) FROM current AS T1 INNER JOIN `current-terms` AS T2 ON T1.bioguide_id = T2.bioguide