My lone RSL has been laying for over 60 days straight. You don't get a perfect egg day with your six?I don't recall reading about a short life span, but did see a couple bits about their egg laying years sometimes being only a couple years...primarily because they lay so many. I have 6 RSL pullets, about 8 months old and am thinking they'll last quite a long time yet. I get an average of about 4 to 5 eggs a day from them. If it falls off too sharply in a year or two, we'll likely cull them. It will depend on how healthy they are...if they're getting decrepit and seem to be in pain, I think it will be kinder to send them along than let them suffer.
Hope your girls do great!