Galvanized pipes last about 40 to 50 years, the range plumbers most often cite, although no agency publishes an official figure. The zinc coating wears away first, then the steel rusts from the inside out. Water chemistry and the quality of the original galvanizing decide whether a given system fails sooner or later.
Galvanized steel was a standard water supply pipe from the 1880s through the 1960s, according to Saint Paul Regional Water Services, so a house from that era with original plumbing is likely at or past the usual range. In Dallas it still turns up in older neighborhoods such as the M Streets and Lakewood. As the zinc goes, rust and scale build up inside and narrow the opening.
That narrowing is why old galvanized lines cause low water pressure across the house, often weaker in some rooms than others, and brown water from the faucet that is worst first thing in the morning. Leaks tend to start at the threaded joints, where the threads cut into the pipe wall.
Lead is the other concern. Where galvanized pipe sat downstream of a lead service line, the EPA notes that lead particles can attach to galvanized pipe and enter the drinking water over time. Only a water test shows whether that has happened.
The honest limit is that age alone does not decide when galvanized pipe is finished; condition does. One section can fail early near its threads while the rest still flows well, and pipe exposed under a sink may not match pipe hidden in the walls. Pressure, water color and leaks at the joints are better guides than the build date, and repiping is the long-term fix, as covered in which old plumbing pipes should be replaced.