first off, fish should be planned to be kept, as mentioned. And returning them is like borrowing, AND moving them is stressful . So you keep a fish for 5 yrs and then take it to the store <stress>, Then someone else buys it and moves it again <more stress>. And if either one of the 2 are responsible, there will be aQ tank involved, thus doubleing the moves at each stop.
2d, many LFS do not accept returns
So, I would wait for the tang, as well.
In the wild, many fish live for that many years, in fact the giant fish, the Blue Marlin, is right about 1 decade per FOOT(a 13 ft fish is well over 100 yreas old). And my dive instructor has been guiding and instructing a particular area and caring for 3 cudas, One loner who is now 6.5 ft(was over 5 15 yrs ago), the other 2 cohabitating elsewhere are over 5 foot in length<not knowing their age they must be old if he has been swimming with them for 15 yrs and they were all pretty large when he first started. As for in captivity, I can name a pair of clowns who are almost 30, a Blu Hipo tang who is over 16 years with the same owner, and another pair of clowns who are 21 yrs ol.
I also kow of a blue hippo tang in captivity who is taken home over 16 yrs ago. and a pair of clowns who are about 30 yrs old and another pair who are 21 yrs ol. the 21 yr old clowns and 16+ yr old tang, I know and visit regularly.