Realty Income is roughly 25% below its all-time high. This could be a good buying opportunity for long-term income investors.The highest Realty Income's (O -0.32%) stock has ever been was just shy of $80 per share, a peak hit in early 2020. And then the coronavirus pandemic upended the economy and the stock market, which fell into a bear market.Unlike the price of the S&P 500 index (^GSPC 0.21%), which has rallied to new highs, Realty Income's share price hasn't recovered. It is still down roughly 25% from ...