Firstly, be wary of anything that claims to improve adult memory:

"In 2014, FTC [Federal Trade Commission] took an administrative action after it determined that advertising for a dietary supplement, that included claims that the supplement was “clinically shown to improve adult memory,” was not backed by adequate scientific evidence."

Source: https://www.gao.gov/assets/690/684620.pdf

Secondly,

"Older adults commonly use dietary supplements despite their costs; however, there is little information available to guide clinicians on their use for cognition. Small trials, which are more prone to bias and chance, may have found certain benefits in these supplements, but larger, high-quality trials have mostly failed to find clinically relevant benefit. "

Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3311304/

So, I don't know what to say about supplements. Perhaps a prescription medication would be a better option. For example, my Ritalin helps (to a degree), and there are non-stimulant ADHD meds like Strattera and Modafinil that are available that might not make one manic.

"[Modafinil] has also seen widespread off-label use as a purported cognitive enhancer"

See here: https://en.wikipedia.org/wiki/Modafinil