This whole process has made me feel so old. I felt quite young and springy until I faced 5 years of medical people telling me over and over again how old I was. I've often joked that if you're at the cancer specialist at 40-45 (I've had cancer a few times) all you hear is sympathetic comments like "you're so young". At the gynae, just the opposite. Which can make it quite enjoyable at the cancer clinic in a perverse way

. (just what the doctor ordered.....a roomful of other patients and specialists telling you how young you are

)
I worry most about that....dying before my child is old enough to take care of themselves. But that's because I'm single...and there'd be so little backup. If I had a partner, not so much because even if something happened to me, there'd be someone to raise them.
But being too old to care for them in terms of physical energy, not so much. I am still a lot healthier (cancer history aside) than many people 10 years younger and honestly, in 20 years I will only be mid-60s (I am 46 now) which is more like people in their mid-50s a generation ago.
I am almost fully accepting that DE will be my own way forward, but in answer to your other question, yes, I know heaps of women who got pregnant (OE) in their 40s. In fact, if I use DE successfully, I will only be a few years behind almost all of my friends (I would likely deliver at 47 or 48). I have friends who fell pregnant at 40, 42, 46 and 47 (all natural conceptions, although the friend at 47 had used IVF for their first at 45). My sister delivered her second child at 43 (also natural conception) after her first at 40. I'm in Australia and I think in comparison to the U.S, assisted reproduction is less frequently used (although still common....with the exception of DE as donors must be open-identity and altruistic only). My reason for mentioning that is that at least some of those friends had been trying for some time (except for the 46 year old...that was a surprise firstborn) so I don't think it was easy, but it can happen. It hasn't happened for me though, despite everything but the kitchen sink (acupuncture, TCM, DHEA, naturopathy, CoQ10, ALA, L-Arginine and other countless supplements as well as 11 IVFs).
If you want to feel inspired, spend some time on the PG after DE or the TTC and parenting over 50 boards (links above). Almost everyone there is at least early 40s, and the over 50s board is full of amazing women. I feel reassured just reading their posts

If it helps, there's a line someone on the DE board used that has stuck with me. She was asking her Mom "how am I going to feel at 75 with a 25 year old child"? and her Mom replied "better than you'll feel at 75 without a child". Everyone I know who's already a parent tells me I will never regret becoming a Mom. I'm betting you won't either....as scary as it is at our age

Good luck
Al