Super agers are a group of people that have the memory recall function of a 40 year old while well into their 80s. This is remarkable. If you're one of these people and your lack of focus at work is actually lack of motivation/fulfillment, these chemicals may not be necessary yet. You didn't specify your line of work but it sounds like it is cognitively demanding so perhaps you can focus on stimulant-related noots. From what I've read on health-related noots (noopept), they have only observable benefits (in research) for people who ALREADY have Alzheimer's or other memory-impairing brain disorders. The wasting is not stopped, but side effects can be mitigated and you can "boost" your brain chemicals so the plaques and tangled proteins are less of an obstacle. But nothing we know of, except perhaps ultrasound, can remove brain plaque.
So TL;DR focus on enhancing chemicals and vary your dosage the first few days to see what works. For noots the recommended dosage is never right lol and you have more leeway with upping the doseage because of the extremely high "overdose" amount for most noots. just watch out for already stacked noots, tripling your dose could also increase your dose of caffeine to unsafe levels.
Speaking of caffeine, and because you've used anywhere from half to a third of your remaining heartbeats, you might consider finding a replacement for it. Theacrine has no tolerance build up and is very similar to the caffeine molecule. The benefits are comparable, however theacrine does not raise your blood pressure or increase your heart rate.
At the end of the day though, nothing boosts mood or focus like exercise. Every capillary flows with blood and the brain gets more oxygen than it does at rest. It's free and it works
But chemically speaking, phenyl-P seems like a good place to start (or just paracetam). If you don't notice effects after 2 weeks you can try oxiracetam which has comparable effects.
Although I've yet to try it myself, semax has a lot of folks on Reddit excited. There are different forms offered on Ceretropic.com but you can shop elsewhere if you just want unmodified semax. It has some research backing its ability to improve test scores (placebo controlled) for multi faceted cognitive tasks (memory, spatial reasoning, mathematics etc)
Noopept is probably a good call for now even though by most standards your brain is still young, rather "not old" lol. But in your 50s or 60s you might notice fast increasing cognitive decline and at this point you'll get your money's worth for "anti" aging compounds like choline supplements, or stacks of botanicals and proteins (turmeric for example).
Some sites list lithium as good for the brain and even go so far as to call it a nootropic.
I'm not an expert but I would be wary of claims about lithium. There is no peer reviewed research to my knowledge showing long term safety or LTP (which could be good or bad depending on the extent of the LTP).