For in-patient age 50 and above, what is their average anti-cardiolipin antibody (IgG) concentration?
in-patient refers to Admission = '+'; age 50 and above refers to SUBTRACT(year(current_timestamp), year(Birthday)) >= '50'; average anti-cardiolipin antibody (IgG) concentration refers to AVG(aCL IgG)
SELECT AVG(T2.`aCL IgG`) FROM Patient AS T1 INNER JOIN Examination AS T2 ON T1.ID = T2.ID WHERE STRFTIME('%Y', CURRENT_TIMESTAMP) - STRFTIME('%Y', T1.Birthday) >= 50 AND T1.Admission = '+'