Hello Gwythiel and welcome to Parrot Forums to you and Adrian.
My first question to you would be, is Adrian actually an olive-headed lorikeet? Or is he an olive mutation of a rainbow lorikeet? The olive mutation of the rainbow lorikeet can be the result of a hybrid of a rainbow and a scaly-breasted lorikeet. The reason I ask this is because it may make a difference in terms of when your bird reaches sexual maturity, which can result in changes to his/her behaviour.
My second question is are you certain he is a male? Most lorikeets show very little difference between the sexes so unless he has been DNA sexed (or until he goes and lays an egg!) you really can’t be certain.
If Adrian is the rainbow/scaly hybrid you may find that he is around about an age where he is entering his first flush of hormones which may cause aggression. He may be trying to fend of what he sees as an intruder and a threat to the bond the two of you share. Lorikeets are particularly fearless and the larger ones like yours can inflict quite serious bites when they get over-stimulated or excited, which is easily done with lorikeets! So in terms of whether this kind of behaviour is “normal”, I would say for an already excitable species experiencing his first hormonal rush and on a sugary diet and who may just be a bit bored if, as you say, “I let him out to play sometimes” and he is cooped up for too long in his cage on his own, then yes its normal behaviour.
In terms of what you can do to remedy it, now theres a $64000 question! More toys, more time out of his cage, more exercise, less fruit, more green vegetables (my Lilly LOVES her broccolini, bok choy, celery, kale and assorted leafy greens) and LOTS of patience on your part. The lorikeet breeding season seems to span about half the year (even more with some species!) so this hormonal thing might become the new normal for you – it certainly has for me with my Lilly!