Welcome to the board. I have lurked often on the playgroup board and am hoping to graduate and be able to join you one of these days (in fact we are potentially matched with a birthmom right now-- so maybe it won't be too far off that I can join!). Anyway, my DH and I are adopting domestically but I just thought I would give you some URLs that could be useful.
The home page for Adoptive Families with lots of interesting articles written by adoptive parents: http://www.adoptivefamilies.com/
BTW, I do know several people who have adopted domestically in their late 40s so that's not impossible either. Here is a link to a thread from the DE board. If you read the entire thread, you will see that these are older parents and this wasn't a concern for the birthmom:
This was independent adoption with an attorney. This is sort of the route that DH and I are likely going to end up going (our situation is a little different). If you are prepared to do your own search for the BM and just have the lawyer take care of the adoption, you can save quite a bit of money. The down side is that you have to do all the initial screening of birthmoms, deal with pregnancy verification and see to it that they get counseling, etc. We are working with a very experienced and well respected facilitator who helps us with all that. She is much cheaper than a pay up front agency or an all inclusive law firm (though lawyers fees vary unbelievably depending on so many factors). Anyway, there are sooo many ways to adopt. You just have to find the way that feels right for you. Have you been able to attend any of the RESOLVE workshops on adoption?
Good luck to you and definitely keep us posted on your progress!