There has been a generational reallocation in the US housing market since the 1990s. Homeownership fell among the young, while older households retained more housing. I document a parallel and underappreciated development: a mortgage boom among older homeowners. By 2019, 40% of owners aged 65–74 carried a mortgage, with an average balance of about $180,000, up sharply from the 1990s. I argue that an expansion of credit supply, brought about by government policy, is a central cause of this shift. From the early 1990s, credit policy broadened access to long‑term mortgages for older borrowers and relaxed payment‑to‑income constraints. To evaluate aggregate consequences, I build a heterogeneous‑agent life‑cycle model consistent with these micro facts. Greater late‑life mortgage access changes how households use housing wealth: borrowing against home equity becomes more attractive than downsizing. This shift reduces turnover and tightens effective supply, raises aggregate housing demand, and crowds younger households out of homeownership. The effects are larger when housing supply is inelastic.