No good way to really differentiate between a 2.5 or a 3.5 yr old. If you enjoy them, no need to sweat their age as they can still earn their keep as the elders of your expanded flock.
We do this with our high production hybrids. Pick up chicks in early spring. They grow and start laying mid summer. Then, the batch from the previous year gets sold in late fall/early winter at around 20 months old. This is more rapid than necessary, we could extend this to an additional year or more probably. But we have a 4-H kid, and cycle through chickens pretty regularly so we have the proper age/type birds for fair season. But, it’s a win-win scenario- we always have eggs bc the young ones lay through winter, and the people who buy the 20 month olds, get healthy birds that are still able to produce really well, and will likely get larger eggs as egg size often increases after the first winter adult molt.
