What is the age gap between the youngest and oldest patient with a normal triglyceride recorded?
age gap refers to SUBTRACT(MAX(year(Birthday)) - MIN(year(Birthday))); normal triglyceride refers to tg > = 200
SELECT STRFTIME('%Y', MAX(T1.Birthday)) - STRFTIME('%Y', MIN(T1.Birthday)) FROM Patient AS T1 INNER JOIN Laboratory AS T2 ON T1.ID = T2.ID WHERE T2.TG >= 200