The Brain, Aerobic, and Resistance Exercise
A comprehensive review of recent research which was published by the British Journal of Sports Medicine (BJSM) found that a combination of aerobic and resistance exercise significantly improves brain health in adults over 50 years, irrespective of the current brain health status of the individual.
Aerobic exercise was found to be beneficial for overall cognitive functioning (processing and functioning skills of the brain) in older adults. Aerobic exercise, commonly known as cardio, is typically low- to medium-intensity exercise for any reasonable length of time. This includes brisk walking, jogging, cycling, and swimming. Tai Chi, a popular form of aerobic exercise, was specifically found to be beneficial for cognitive function as well.

The Main Takeaway
An exercise program with both aerobic and resistance-type training, of at least moderate intensity and at least 45 min per session, on as many days of the week as possible, is beneficial to cognitive function in adults aged >50 years. So a daily (or at least every other day) workout session comprising of about 20-25 minutes of strength training using weights and machines, followed by 20-25 minutes of any form of cardio would have a good impact on your brain health.
A physiotherapist or exercise trainer can help you with building a program most appropriate for your health needs, taking into account any difficulties or specific goals you may have.
Read and download the full review at BJSM here: Exercise interventions for cognitive function in adults older than 50: a systematic review with meta-analysis