Something which may interested you from Imperial Armour 9 - The Badab War (Note, this is a direct extract, and thus has spoilers. I have forgotten how to do the spoiler tags, but it is nothing serious, anyway.)
Worthy of note to this record is the nature and history of Knight-Commander Stibor Lazaerek, Grand Master of the Fire Hawks during the Badab War. At the outset of the conflict, Lazaerek was more than six centuries old and in failing health thanks to numerous war wounds accumulated in his long career.
This, to me, suggests that overtime the Astartes do begin to fail in health. I imagine that it is particular to each Chapter and their Bloodlines, with Blood Angels seeming to have more longevity than say, an Imperial Fist..
Nyctophobia- Fear of the Dark Angel.
"No one ever spoke about of those two absent brothers. Their separate tragedies had seemed like aberrations. Had they, in fact, been warnings that no one had heeded?"
'Killing a man is like fucking, boy, only instead of giving life you take it. You experience the ecstasy of penetration as your warhead enters the enemy's belly and the shaft follows. You see the whites of his eyes roll inside the sockets of his helmet. You feel his knees give way beneath him and the weight of his faltering flesh draw down the point of your spear. Are you picturing this?'
'Is your dick hard yet?'
''What? You've got your spear in a man's guts and your dog isn't stiff? What are you, a woman?'