You can use all()
:
my_list1 = [30,34,56]
my_list2 = [29,500,43]
if all(i >= 30 for i in my_list1):
print 'yes'
if all(i >= 30 for i in my_list2):
print 'no'
Note that this includes all numbers equal to 30 or higher, not strictly above 30.