After dropping in childhood, the human death rate in adulthood rises exponentially, doubling every 8 years like clockwork until the number of survivors is so low that the statistics breaks down (although there is weak evidence of a "deceleration" at very high age). Most animals follow similar curves, even if they live very long the shape of the curve is similar.
But then there are naked mole rats. They have an almost constant mortality with age in adulthood. They do age slightly in terms of activity and appearance, which we will neglect for world building. Also we will neglect all the other bizarre features such eusociality, CO2 tolerance and much more.
Forever 21: Suppose we have contemporary human society, but there is no aging in terms of chronic diseases or loss of physical/mental function. Instead every year there is a 1% chance of death by "natural causes" in your sleep (no matter how much or little sleep you get per night, the risk is 1%/year). We still have non-intrinsic deaths/impairments such as injury, infectious disease, starvation, heat stress, etc; although moderate insults are more survivable because every adult has a 21 year old's body. The average life expectancy will be 100 years (ignoring higher death rates in childhood), but people living 1000 years are not unheard of. Society will be different, but how?
Medicine: Medicine will be about trauma, mental health, and infectious disease. IRL naked mole rats come close to having no other needs, which is idealized to be always true in my world. As medicine costs a enormous amount of money (particularly in the country where 40 degrees is a cold temperature), this will free up a lot of resources. But if it always had been this way, would we know any different?
Employment: Retirement is not an issue. No saving up a nest egg, no anti-old age discrimination based on health or proximity to retirement. I imagine there would still be discrimination based on the tradeoff between "youth" and "experience"? The tech industry with their "90's kids" while the most traditional facets of banking advertise 1000 year old CEO's and their knowledge of Latin or Sanskrit.
Housing: A higher renting to buying ratio seems likely, as the idea of settling down and retiring is archaic.
Relationships: Most people may still want to marry within their "childhood decade's" culture. However, more cross big age gaps than today's society, and the rare 500 year-old is sought after by so-called "history-chasers". Death usually means remarrying. Being a parent never gives way to being a grandparent even if the latter occurs. Losing parents in childhood is a high (~18%) risk so children rely on extended family networks more than WIERD culture IRL.
Immigration: It may be less (stricter laws) if there is less need for young people to move to old countries.
Anachronistic technology: Older technology may be in use longer. Some are used to their typewriters. The greatest benefit I see is more walkable cities, as there are enough people who aren't used to modern traffic. A potential drawback is an even worse version of being stuck with out-of-date methods due to the practices of the (very old) powers-that-be.
