The maximum term length for a buy-to-let mortgage can vary by lender, but it's typically around 25 to 35 years. For older borrowers, the term may be adjusted so that the mortgage concludes before or around the borrower's retirement age, usually considered to be around 70 or the age specified by the lender. Specific terms can depend on the lender's policies and the borrower's financial situation​.
When considering applying for a buy-to-let mortgage, especially as an older borrower, it's advisable to consult with a mortgage broker or financial advisor who can offer tailored advice based on your circumstances and help navigate the various lender requirements.