80 years? I would date its birth as 1968-9 (Veneziano), it’s hard for me to imagine calling prior work than that as “string theory”. But never mind that—the bigger problem with this (quite common) argument is that everything about quantum gravity, not just string theory, has avoided testability because our other theories are too good, and because we’re limited to doing experiments on Earth with equipment built on human scales with human budgets, and that’s just not where quantum gravity would naturally make itself known. So really this argument just suggests we shouldn’t study quantum gravity at all. Maybe that’s your actual opinion—it’s a waste of time if we can’t access the Planck scale, we should table it all and sit on our hands until we can. But string theory really is quite interesting to study, stuff like AdS/CFT is just really surprising and magical when you get what it’s about, and it would be a real pity to not pay the meager salaries of theoretical physics just because of pessimism. String theory is so far from fully understood! It’s actually…really hard!

BtW I think you got this 80 years number from looking at the earliest date on the Wikipedia page. You might want to read it more carefully. Not everything leading up to string theory is string theory.