My mum was just shy of her 40th birthday when she had me, her one and only, after being told she couldn't carry a child full-term.
They were great parents, maybe they were a bit old-fashioned compared to some of the younger parents, but then again maybe they were just more settled and calmer. There's pluses and minuses to older parents and personally I think they tend to cancel each other out, so I wouldn't fret about that angle of it.
I loved being an only child, didn't want a brother or sister. It was great having my parents to myself. I think it made me become more independent and in a roundabout way more sociable as I grew older because I don't ahve family to rely on so I have to make the effort to get to know people.
Anyway, you cannot predict what your child/ren will turn out like wether they have a sibling or not. I'd stick with having a child or not based on what you want.
-------------------- I have the talent of single-minded determination and foc....hey, look, dog!