how to open old aperture library

To open an Aperture photo file, you will need to have the Aperture software installed on your computer. If you have the latest update of Aperture 3 installed, you can simply open the software and then open the photo file within the application. However, since your file is 125 GB in size, it may take some time to load depending on your computer's processing speed and available memory. You may also want to consider freeing up some space on your computer or using an external hard drive to store the photo file.

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Is the system version stated below your question still valid? macOS 12.6?

macOS 12.6 is the last system version, where the Photos.app can still open an Aperture Library and convert it to a Photos Library, as VikingOSX recommended. If you already have upgraded to macOS 13 Ventura, you can only import the photos and videos from your Aperture Library into a Photos Library. This will save the media files, but you can no longer save the structure of the Aperture Library, the albums, projects, and folders and keywords.

To import the items from an Aperture Library to Photos launch Photos, then use the command "File > Import" and select the Aperture Library.

Apple's Photos application on Monterey can open an Aperture library. See this post.