何かのようなもの
select case when max(t1.age) > 60 then 'RED' else 'GREEN' end table1_age,
case when max(t2.age) > 60 then 'RED' else 'GREEN' end table2_age,
case when max(t3.age) > 60 then 'RED' else 'GREEN' end table3_age
from (select max(age) age from table1) t1
cross join (select max(age) age from table2) t2
cross join (select max(age) age from table2) t3;
また
select 'table 1' tabl,
case when max(age) > 60 then 'RED' else 'GREEN' end
from table1 t1
union all
select 'table 2' tabl,
case when max(age) > 60 then 'RED' else 'GREEN' end
from table2
union all
select 'table 3' tabl,
case when max(age) > 60 then 'RED' else 'GREEN' end
from table3;