hens not laying

I still feed my old timers in retirement on layers - they can still lay the occasional egg 

Layers pellets aren't good for young chicks because the calcium can build up over time.  But as your hens are at the 'other end' of their lives it's very unlikely there will be a chance for the calcium to build up to harmful levels.

In fact, there is an argument that older hens (like older people) can benefit from extra calcium to keep a healthy bone density in their old age.

Also, when did your hens lay their last eggs?  It's possible they are just taking a break and may get back to full production after a little R & R.

Good on you for looking after your hens during their 'retirement.'