there's no upper age limit - it depends on goals, stresses, frustrations and effects on family
If ADHD was only about work, then I suppose possibly not, but it's also about enjoying reading, listening to your partner, following through on intended tasks, managing money, avoiding impulsive decisions that don't tend to work out. It's about learning new things and exploring new opportunities. You may be retired but your'e not dead!
It's about being less anxious, being resistant to depression, and improving quality of life, so yes, there's definitely value in exploring possible ADHD.
There is no contraindication to treating ADHD at any age, although some health problems that are more common in people 65+ could be an issue, for example atrial fib.
Interestingly coronary artery disease is not a contraindication and while we need to be more cautious when there's hypertension, it's not a contraindication.
I do start treatment for people in their 70's and the highest I've heard of was someone who was 97.