male or female? males are likely to go on for longer as there's less physical strain involved in the whole process, but as for an exact age i'm honestly not sure and IMO it goes a lot on the individual snake. if a female has been bred every year from being 3 years old i'd want to retire her from breeding earlier than a female that's bred alternate years or infrequently. i'd also use how well they recover from being gravid as a guide, if she struggled to regain weight or dropped weight drastically after laying i'd have a serious think about whether to breed from that individual the following year
cornsnakes, ratsnakes, bullsnakes, boas and day geckos
a female can breed as young as 12 months, but this is way too young to be healthy. ideally she would need to be in good condition, 3 yrs old, 300+ g, 3' length.
males can be bred from 2 yrs old, any much younger he will be firing blanks