I'm actually contemplating it at the moment. I'm 49 but would be 50 by the time a baby arrived, if we were successful.
I had a baby at 46, 5 weeks before I turned 47 and it's the hardest, but absolutely best thing that's ever happened to us. He's my first and we went through IVF and have another embryo, hence the contemplating now.
I know people talk about the exhaustion, but my life really started with having this baby. I found out I have an underactive thyroid, symptoms of which I've had since puberty, the most obvious being feeling indescribably exhausted all the time.
Having treatment is like waking up after 30 years, so I'm just constantly amazed at how much more awake I feel now than in my teens, 20s and 30s. I definitely couldn't have done this then. It probably accounts for never getting pregnant before as well, so having this opportunity at this point is something I pinch myself about regularly. It the most wonderful and fascinating thing to watch him grow.
We're conscious that as (much) older parents we might pop off sooner that our son's friends' parents (although my older parents are still going and living independently whilst I have friends whose much younger parents have died). So a sibling would be someone else to have that connection to the past with, support and friendship throughout life.
But it may not work, they may not get on etc. So, we'll see. The main cons are that my husband's work takes him away a lot, we don't have the grandparent support that a lot of parents have and my own career is just taking off. I'd feel guilty having more childcare help for this baby than I did with my son, who I've been with almost constantly so far.
It all depends on your personal circumstances I suppose, but good luck if you decide to go for it.