I had my third at 36.
I have a funny story about a mom's age.
When I was 9 I asked my mom how old she was. She had me at almost 40, so she was turning fifty shortly. At 9, 49-50 seemed ANCIENT to me. She did not want to tell me but I insisted that she tell me the truth. She says I told her, "I can handle it!" Well, she told me she would be turning 50 and I nearly had a heart attack. I seriously was sick with stomach aches about it, thought it was the beginning of the end. All of my friends parents were young, maybe mid 30's on average, some a bit younger than that and some a bit older, but overall 35 was pretty average and she seemed so old to me after that. I always was worried about her, and looked at her wrinkles and got scared. She is turning 80 in January so she is doing well. Sadly, though, my dad died of cancer a few years later and then I really got scared, because she was all I had left and if she died I would be an orphan.
My son always tells me I am the second youngest mom in his grade. The youngest is a month younger than I am. I also look pretty young so sometimes people find it hard to believe I have a 14 year old. For my mom to have a kid at that age in the 1960's was rare, of course it is not rare today.
I think in today's world as long as you are healthy it is no problem to have a child at close to 40. You must make that extra committment to being healthy and you would likely need to see a high risk ob, but if are fit and do not smoke and eat well, I think it is really so easy to manage. They will likely run lots of tests and screenings, so do not worry, you will have a lot of information. I might recommend a CVS instead of an amnio if you would be inclined towards that type of test (some people are opposed and do not want them). I do not agree with people having kids super late, because of something happening to the parents.. I have heard of rare cases of women having kids at 50 something and think, they may not make it to see the kid off to college, and while at 18 a person is likely able to handle things in life on their own, it is still sad to me...