Gold toning is pretty standard practice with albumen prints. I've tried selenium, and it works as well, though I don't find the tone as attractive as gold.

Aged albumen is generally considered to be a good thing. I find it has a more uniform consistency than fresh albumen. I don't know if it makes a difference in terms of yellowing, but perhaps paper albumenized with aged albumen will start out yellower, so it will change less over time. Old albumen is yellower than fresher albumen.