Aging related: there's been a good bit of research on using creatine monohydrate supplementation to slow mental decline. It's been shown to slow the progression of Parkinson's, Huntington's, ALS, and AD. There's a good survey article here (PubMed) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4304302/
Thinking about it, this should be unsurprising as the phosphocreatine cycle is important for mitochondrial ATP generation - and our ability to recycle creatine drops by about 8% each decade after we turn 30 - and many of these CNS conditions (as in 'the ones I've tracked research on') have associated mitochondrial dysfunction. There's disagreement over whether that's causal. Go read the article.