For the first part of your response, I will say that I don't think it matters if I actually try to shield or not, in terms of the brightness. Things are always trying to get my attention, as I have shared in other posts here. So I don't really think shielding makes it any worse, any more than a very tall person trying to crouch down when they walk. It is readily apparent that the person is tall. So they might as well stand up!
I really can't say how long I have had this ability. I never thought of it as an ability at all, just accepted it like being left handed or near sighted. I do try meditating but find it difficult to sit still for long. I like being active and in motion, lol. A rather amusing example is this:
A few days ago I had an EEG test done while awake. As I lay there I felt horribly bored because I wasn't allowed to move about or talk, so I started trying to remote view different rooms in the hospital for amusement. The test came back saying I had been asleep and dreaming. So I couldn't even stay still mentally for the test!