Congrats on a 20yr old sun! My Skittles is 5.
As for your question. Yes and no. I have a 20 year old cockatiel, Peaches. She used to lay eggs a little bit and then stopped for years. Then the spring after I got Skittles she started laying them over and over.
I don't think there is a cut-off age for laying eggs. But the older they are, the more concern there should be. Laying an egg is very stressful for a bird (regardless of age) just like childbirth is for women.
The primary concern should be that they are getting enough nutrients to make up for what they lose with each egg laid. It is also vitally important that an egg-laying bird have a cuttlebone (to provide calcium).
If it becomes a habit of egg laying over and over for a long period of time, I'd check with a vet. It could be a hormone imbalance.
Birds can lay several eggs in each clutch. If they lay more than 5 or 6, I'd take her to the vet.
When was her last vet checkup? I was very concerned with Peaches when I took her this past spring. But the vet said she is as healthy as Skittles. I feed Peaches organic harrisons so she definitely is getting her nutrients.
If you are that concerned, a vet checkup can't hurt.