Hi Stickmeup; if you have comerical hens (farmyard red or black (or grey these days!)), then after laying for 14-16 months, then they are definitely coming towards the end of their laying days.
Commerical red hens are considered "spent" after 80 weeks, and it at this point when the farmers get rid and start a new batch off.
Also, just in case you weren't aware (and I apologise if you are), 3-4 years is considered a very good age for commerical hens, though you do get the odd one living for up to 8 years... though most will stop laying by the time they are 2 years old.