How well defined are the boundaries and how many years does a
normally, in average, have in DSA5?
(Page numbers are for the german version)
Human: about 80 years (sometimes 90-100 or above) (p.90)
Elf: until they fulfilled their purpose in life (then they pass away within days) (p. 91)
Half-Elf: about 100 years (their appearance stays young until shortly before they die)
Dwarf: about 300-400 years (it is not unusual that they get even older)
Orc: about 40 years (p. 27, "Aventurischer Almanach")
(While the ruleset changed, the world is the same, so I would assume that the life expectancy of the older books stays correct)
Halflings do not exist per se, but you could compare them to the "Hügelzwerge" (Hilldwarves), which left the mines, and are described as good-tempered and buoyant. Thus, see dwarves for their life expectancy.
Gnomes aren't a race either. It is a disdainful way to call a "Geode", which is a dwarven druid/mage with focus on elemental magic.
Golems are constructs and created through magic, so there is no real life expectancy.