Can I see Apple health data from over a year ago? It's nearing a year since I've been actively using the health app and I'm worried that all my logged runs and weight changes will be lost. Does anyone know if is data is saved somewhere (eventually, maybe, so I can visualize changes over e.g. five years, on the iPhone 15s).

If not, is there an alternative system where I can import my weight data to manage it over a longer course?
The health data is not deleted beyond one year, but Health.app doesn't show graphs beyond one year. You can view the raw data by selecting the metric and choosing Show All Data.