Like a number of the sage mamas in this group, my spouse and I have a big age spread between our children: we adopted our daughter a year ago and she's now 21, and we're expecting a baby in late November. I'll be 41 when he or she is born and my husband is 50. We had fertility problems and had been married for 17 years before succeeding with this little one--yay! Our daughter, Katey, is excited to be a truly big sister: all of the enjoyment of a sibling without the hassle of having to raise the squirt.
Older parenthood runs in my family: my grandmother was 45 when my mother was born (her only child); my mother was 34 for me and 36 for my brother. My parents are now 85 and 76 and are doing well living independently, but my mother is becoming increasingly disabled (she now gets around primarily in her wheelchair, although she uses a walker in the house), and I've reminded them multiple times that they are welcome to come live with us when they feel they're unable to keep living on their own. However, my mom is very active in her community (they are both retired teachers and she teaches at the teachers' union retirement center) and has many friends, so she is not eager to move (they live on the East Coast and we're on the Oregon Coast).
Fortunately or unfortunately, depending upon how you think of it, menopause hits late in my family; my mother was in her late fifties before she had her very last period. This is so pesky--another ten or fifteen years of menstruation?! (That's been one of the nicest things about pregnancy: not having a period!)
What I anticipate appreciating about older parenthood is the greater level of patience and understanding we now have, as well as the fact that we are established in our work lives--and we can bring our offspring to work! What concerns us is that because our parents are aging, they won't have as much time to spend with their grandchildren as they would've if we'd been younger when we started our family. We do have some concerns about not being as energetic in our 40s and 50s as we were when we were younger, but they're not huge concerns, as we're highly physically active and perhaps fitter than those half our age. (We ride our bikes to work, 24 miles round-trip, and my spouse regularly challenges younger riders in Lycra--and often wins!)