Is a five-year-old personal loan too old to sue over?

A limitation period is not a gate the court closes for you. It is a defense, which means a filing outside the window is accepted, processed and heard, and if the other side never mentions it the case can run to judgment on its merits. That produces an honest but uncomfortable answer: a five-year-old written loan is unenforceable against anyone who knows to object and enforceable against anyone who does not. As a basis for spending a filing fee and one of your two annual slots, that is thin, and it is worth being clear-eyed rather than hopeful about it.

Where these are occasionally rescued is the start date, which people routinely get wrong in their own disfavour. The clock runs from when repayment was missed, not from when the money was handed over, so a loan advanced six years ago with repayment due three years ago may sit comfortably inside the written-agreement window. Where no repayment date was ever fixed, it generally begins once you asked for the money and were refused, which can be surprisingly recent. What is genuinely risky is trying to manufacture a fresh start by coaxing a written admission out of them. The analysis is technical, the downside is real, and it is a conversation to have with an advisor beforehand rather than afterwards.