I R actually a twin, born to a 34 year old mother. Many people are unaccountably interested in this reveal. Their first question, even after I've claimed a twin sister, is to ask "Are you identical?" Usually my vague circulatory hand gestures about the chest are sufficient to answer the question; but not always - the idea of having an alter ego or doppleganger is important for many people. Obviously I've written about twinning before. Twins are slightly more likely to be left/right-handed discordant. In humans, it is not generally true that boy twins weigh heavier than than their female womb-mate [although that was true for me and m'sister]. Nobody has suggested that we might not be [genetically] related although we really don't look much alike: the audit trail since the midwife attached wrist-bands has been pretty solid.
I am currently reading The Newborn Identity by twisteddoodles aka Maria Boyle PhD. It is the story of getting preg with twins, delivering same and sustaining them through their first year out in the dry, cold world. It's funny and informative: I thank the gods for sparing me the first, preg, half of that ordeal and the patriarchy for giving me a pass on much of the second part.
Identical twins separated at birth are another facet of the fascination with twins. And there have been some remarkable studies of the peculiar aspects of life which are shared by twins who have had no common upbringing but 100% of their DNA is shared. On the far side of that world are people who have a striking physical resemblance [often shown up by social media] but have zero identity by descent - Niamh Geaney is a well trotted example. She is a poster-girl for twinstrangers.net a site which pretends to help you find someone who could act as your Kagemusha if you feel you're not long for the world.
YMMV, [give it a go, it's free] but my experience is that A Lot more people need to register for the site before it's going to work for old white patriarchs. Heck, they can't even get the [steel-grey] eye-colour right.