Here are some examples of some old (non-pu'erh) teas....A 70s oolong.An 80s black tea.
They're both spectacular... and unfortunately both out of stock.
But yes, if properly stored, some teas can get better. For pu'erh, this means storage in open atmosphere. For other teas, it appears to mean air-tight storage.
I'm not sure if any of that applies to greens (or at least, I'm not sure I've seen decades old green tea, whether Japanese or Chinese).