In an several earlier books it was referenced that wizards heal completely unlike us normal mortals.  with this complete healing harry should never feel the minor pains of ageing that mortals feel because his body can fully heal from all the strains and damage done to it.  If this is the case why did he feel so good without a body being absolutly free from all the small nagging pains of getting older that we tend to ignore?  he should not have had any except for current battle damage.