Still laughing at posters who say they don't know anyone over the age of 32/35/38 whatever who's had a child, as though that's a reason not to do it. It seems blindingly obvious to say that no one can make the decision but you, but here's what I think anyway.
I've never seen a thread on here asking whether AIBU to consider having a child because the OP was obese, or disabled, or on benefits, or gay, or found themselves in any other circumstances other than the stereotypically 'perfect' family set up that some of the above posters seem to think they have. I imagine many people would find the idea offensive. But age discrimination is apparently OK???? 
If anyone is suggesting that 42 is "too old" based on some perceived lack of energy to parent a little one - I wonder what they'd make of thousands of women in their forties who are nursery nurses, teachers, paramedics, midwives, or anyone working in any other occupation apart from a part-time job behind a desk who can go home early for a nice lie down?
As for the point that you might die before your child grows up
. Anyone of us could die as tragically young as Rebecca Ellison (Rio Ferdinand's wife, age 34) or live to be 100 like my granny. You can't plan your life like that.
Many (perhaps most) women are still perfectly fertile at 42 - you won't know until you try. Yes its true that the risk of miscarriage is higher than for younger women, but equally its not as if miscarriage is the preserve of women in their forties. Its also true that the statistical risk of genetic abnormalities is higher, but there's excellent antenatal testing available. Its obviously an intensely personal decision as to what course of action you might take if there was 'bad news'.
I got pregnant (first try) at 43 and had my DD at nearly 44. I find it mildly upsetting that there are people on this thread who would probably say she should never have been born. I also find it comforting that its nobody else's f*ing business. She's now 21 months and is beautiful, clever, physically athletic, way ahead of all her milestones and yes of course I am biased because I adore her.
So I think the only answer should be, if you want a child, try to have one, if you don't, don't.