I think I would be more confident flying N641UA than any other 767 in the fleet right now. The length of the repair corresponds to the amount of work done on the airframe... which was extensive. A fair amount of corrosion-related repairs that weren't directly occasioned by the bounced landing, plus newly-manufactured parts, inspections, etc.

This is hardly a one-off for Boeing as they have done this repair over and over again on the 763 for the last 25 years or so, and as far as I can tell, all have been successful. The propensity for the fuselage to buckle at exactly that station on a PIO/bounced landing + NLG touchdown is a flaw inherent to the design of the 763, unrelated to the age of the airframe in question.

As it relates to N641UA, yes it is an "old" airframe in person-years, but at present utilization levels it has no fewer than 6-7 years of "life" left before reaching its certificated design limit... which is well short of its actual (tested) structural life limit. The question is at which point the cost to maintain becomes so prohibitive that it negates the cash flow the asset can generate in service, especially considering how valuable the 767's core mission in the UAL network has become in the last few years. I think the proof is in the pudding.