How old is too old to adopt a newborn

You know, I am 43 and DH will soon be 46. We have already adopted 3 children and are pursuing adoption again. I have also thought about all the negative things that can happen....my biggest fear is dying before my children are grown. But, that can happen with young parents as well. We are active with our children, lots of outdoor things, camping, travel, swimming, etc. The only thing I find difficult is the fact that most of our friends have children much older than ours...so not many play dates with them. lol Having said that, when we do visit our friends, there are many older kiddos who love to dote on mine. lol We do attend play groups whereby the younger ones get to play with other children their own age. I had a relative who gave birth at the age of 50. She lived long enough to see her grandchildren graduate from high school....so you just never know. :)