My term embarrassingly is a function of auto correct not noticed because of the influence of medical drugs for a tooth infection. Please mentally replace SLA for SLC while I hang my head in shame.
Applying arbitrary limits based on gut feeling is never helpful, you're correct. But those that do would logically draw a line past a date where the number of tanks above an age drop off in popularity
Equally cylinders are so in expensive that apart from sentimentality there is little justification in requiring that an old cylinder be allowed to continue in service. Keeping a cylinder for 20 years means its cost is roughly $20 per year (an unpopular view I'll accept)