Hi A.,
I will be turning 36 in less then a week, and my husband and I are seriously thinking about having another child. We had our first when I was 34. In addition, I have one sibling ... a sister, who is 12 years younger then I.
As far as what other people will say.... no one will say anything. Older moms are very very common these days. I know SEVERAL moms who are all my age or older who have children around my daughters age. So that really isn't an issue honestly.
I can see how you would have concerns. You have a lot on your hands already with your oldest son. However, as someone already said, I do see each child as a gift. I do believe they each deserve the right to life. If you really feel you can not handle raising another child, adoption is a great option. A friend of mine just adopted a little boy through an open adoption. She and her husband have been trying unsuccessfully for more then 5 years to have a child and adopting this little boy has brought more joy to their lives then I can ever explain.
The open adoption allows the birth parents to receive updates, photos, and schedule visits from time to time in order to see how their little boy is growing and how happy he is. There is no confusion over who is 'mommy and daddy' ... the open adoption is just a way for the birth parents to see they made the right decision and their little boy is growing, happy, healthy and loved dearly. My friend said at first she was very cautious of an open adoption, but now feels it actually helps relieve the biological parents fears and worries and thwarts the potential that they will want the child back because they see how loved he is... and say so.
I will say, for myself, having a sister is 12 years younger then I was great. We are, and have always been very close. There was never any sibling rivalry or anything like that. I helped take care of her and when I was older we would have our special days together and I would take her out to lunch or someplace special. We had a great time together. I think if you talk with your 12 year old and explain the situation and are open and honest with him about what you will need from him you most likely will find he will be a great help.
Financially, yes... kids are expensive. But there are always ways to get through that. I truly believe where there is a will there is a way.
So, you do have a lot to think about ... but I think you have some very good options that go beyond terminating the pregnancy (and you didn't even mention if that was an option for you... hopefully it is not).
Take your time to make your decision, talk to all the people in your life this will affect and then make a decision together.
You CAN do this. Sometimes the unplanned things are our greatest adventures.