There are so many variables here it was really hard for me to decide on an answer. I voted 15-20 i feel like a well made tank with exceptional care etc can last longer but id expect the average tank with average care to hopefully last this long. Ime one of the big factors is size of the tank and the ever stressful task of moving said tank. The more you transport a tank the more you risk damaging it, even if you dont realize you jared the silicone. Then the larger the tank the more of a pain transportation is and the more stress etc on each seam. Ive seen 5-10 gallon tanks handed down through generations in my family, my 55gal got a reseal after 10years though because the silicone was just pealing off in huge pieces after sitting empty for a few years. And ive seen a 100gal tank set up 10years+- and get moved to only last another month tho there was no apparent damage.. just some examples. Id expect longer if the tank was set up day 1 and never moved though vs someone who relocates regularly.