I have 14 year old pv panels operating at 45%. Guarantee life spans are guesses.
Do you clean your solar panels? Mine, admittedly the oldest of which are only 4 years old, seem to do as well as new. I clean them once or twice per year. And they have a warranty to operate at at least 70% capacity 25 years from now (linear decline, so call it no more than 1% per year decline).