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Most of my book collection in Hong Kong, all 1.5Tb of it, is now in audio format. If you listen to Haldeman again keep a close ear/eye on his numerous returns to what is essentially 'Central Command' and the changes mankind undergoes in his timeline, which in Earth's timeline is centuries - he deals with medical advancements to re-grow limbs, issues of sexuality and finally gender.

Again, I also recommend John Scalzi's 'Old Mans War' series, which has an interesting premise, namely, OAPs volunteering to join the Colonial Military post 70's, being given new youthful bodies and going off to fight alien menaces - some good twists in this with regards his wife.