Length of credit history: the factor only time can build

Of FICO's five factors, length of credit history is the strangest to manage: it's 15% of your score, nothing you do today can add a single day to it, and yet careless moves can subtract years in an afternoon. It's also the factor that quietly explains why two people with identical habits score 60 points apart — one has a 2016 card anchoring the math and the other torched hers in a fit of wallet-cleaning. Here's how the clock actually works and how to stop breaking it.

What the models actually measure

• Age of your oldest account — the anchor. A 15-year-old first card is one of the most valuable objects in your financial life, whatever its rewards rate.
• Average age of all accounts (AAoA) — every open account's age summed and divided. New accounts dilute it; time repairs it.
• Age of your newest account — a very recent account signals fresh credit-seeking, and some models look at how long since your last open.
• Ages of specific account types — how old your revolving file is, how old your installment file is.

Closures: the delayed-fuse version

Closing an account doesn't hurt your history immediately — a closed account in good standing keeps reporting and counting for roughly 10 years. The damage is scheduled, not instant: a decade later, the account falls off, and its age exits your average all at once. This produces the characteristic mystery drop — 'my score fell 25 points and I did nothing' — when a card closed in 2016 silently exits in 2026. Negative closed accounts leave earlier (seven years), which at least means derogatory departures are usually score-positive. The practical rule: closures are a debt to your future average, payable in ten years, and the oldest accounts carry the biggest balances.

What thickens the file besides time

Two legitimate accelerants exist. Authorized user status on an old, clean account imports that account's age into your file at most issuers — the standard way parents gift a decade of history to an 18-year-old, and a real (if smaller) boost for any thin file. And keeping paid-off installment accounts in good standing on the report costs nothing — a finished car loan keeps contributing its age for its ten reporting years. Beyond those, there is no lever: no product, service, or trick adds age. Anyone selling 'aged tradelines' or 'seasoned files' is selling either an authorized-user rental (detected and discounted by modern models) or fraud.

Managing the clock deliberately

1. Designate your oldest card a lifetime holding: one small recurring charge, autopay in full, reviewed annually, never closed casually. If it carries a fee, product-change it to a free version — the account and its birthday survive a conversion.
2. Batch your applications into eras: opening three accounts across a focused six months, then nothing for two years, beats a steady drip — the dilution happens once and heals continuously.
3. Time new accounts against your life calendar: every open should be 9–12+ months before any mortgage or major loan, so the age dent and inquiry both fade before pricing day.
4. Before closing anything, check its opening date against your file: closing a 2022 card is a rounding error; closing your 2008 card is scheduling a 2038 problem. Fee-driven closures of old cards deserve a downgrade attempt first.
5. If your file is young, accept it: a 3-year file with perfect payments and low utilization scores respectably and improves every single month. Age is the one factor with a guaranteed positive trajectory.

The bottom line

Length of history is compounding you can only start, protect, and dilute — never buy. Anchor the file with a permanent oldest card, batch your opens, respect the ten-year fuse on closures, and let every account's birthday do the quiet work. The best time to start the clock was years ago; the second-best is the next account you were going to open anyway, held forever.