The pension schemes of many countries offer the option of retiring early, at the price of reduced monthly pension payments. In that sense, you’ve bought the early retirement and paid for it with reduced pension entitlements. I know the German statutory system offers this option. I understand the OP’s question, however, as asking whether a more direct purchase option exists, whereby you pay a lump sum into the pension scheme in exchange for the possibility to retire early. This, too, is an option that exists in the German system. Essentially, you pay a lump sum, and in return you’ll get points which are, in the formula used to calculate your pension payments, equivalent to the points you earn for the years during which you’ve contributed to the scheme. I personally think it’s a terrible investment, and to my knowledge it’s not an option that is used very frequently, but it exists.