Live Up is a service funded by Department of Health, Disability and Ageing. It has lots of tips and ideas about healthy aging, including staying physically active and social: https://www.liveup.org.au/
Health Direct is a government funded service that provides health information and advice. The article on mental health in older Australians has a symptom checkers: https://www.healthdirect.gov.au/older-people-and-mental-health
The Black Dog Institute has a fact sheet about depression in older people here: https://www.blackdoginstitute.org.au/wp-content/uploads/2022/06/Depression-in-older-people.pdf