Hi HariS,
Like you I also think highly of Capitol Bedding and it’s always refreshing to see a manufacturer that is transparent about the materials inside their mattress.
While there is no way to quantify how long any mattress will last for any specific person or predict exactly when you will decide to replace it because it is no longer suitable or comfortable for you (because this is the only real measure of durability or the useful life of a mattress that really matters) because there are too many unknowns and variables involved that are unique to each person … if a mattress is well inside a suitable comfort/support range and isn’t close to the edge of being too soft when it is new (see post #2 here) and you have confirmed that it meets the minimum quality/durability specs that are suggested in the guidelines here then it would be reasonable to expect a useful lifetime in the range of 7 - 10 years and with higher quality and more durable materials like latex or higher density memory foam or polyfoam (in the comfort layers especially) it would likely be in the higher end of the range or even longer and the chances that you would have additional “bonus time” would be higher as well.
Since you are in an average weight range and the specs of the mattresses are just under the guidelines I would normally suggest it would be reasonable to “expect” that it may last you a little less than 7 - 10 years although the only way to know for certain how long any specific person will sleep well on any mattress will be based on your own actual experience.
Phoenix