A 16-year-old and their grandparent could both be investing — but they should almost never use the same mix of investments. Asset allocation is simply how you split your money between things like stocks and bonds, and your age (really, your time horizon) is one of the biggest factors in getting that split right.
What Is Asset Allocation?
Asset allocation is the big-picture decision of how much of your money goes into different categories: stocks, bonds, cash, and sometimes other assets like REITs or commodities.
Stocks tend to grow faster over decades but bounce around a lot in the short term. Bonds are steadier but usually grow slower. Your allocation is basically a dial between "grow fast but bumpy" and "grow slow but smooth."
Why Time Horizon Matters More Than Age Itself
The real reason age matters is time horizon — how many years until you'll actually need the money. A 16-year-old saving for retirement has 45+ years for the market to recover from any crash. A 64-year-old about to retire has almost no time to wait out a downturn.
That's why teens can usually afford to be heavy in stocks — even 90-100% — since you likely won't touch this money for decades, giving it time to ride out market crashes and corrections and benefit from that long average growth runway (often modeled around a 7% average yearly return before inflation — real returns vary and aren't guaranteed).
A Common Rule of Thumb (and Its Limits)
You may hear the old rule: "subtract your age from 110 (or 120) to get your stock percentage." A 16-year-old would get 94-104% stocks. A 60-year-old would get 50-60% stocks.
It's a decent starting point, but it's not perfect for everyone. Someone who panics and sells everything during a crash might actually do better with a slightly gentler mix, even if they're young — because the best allocation is one you can actually stick with. Your personal risk tolerance and goals matter just as much as a formula.
How Allocation Shifts as You Age
As people get closer to needing their money — for a house down payment, college, or retirement — they typically shift gradually from stocks toward bonds and cash. This reduces the chance of being forced to sell stocks at a bad time, like right after a crash.
This gradual shift is exactly what "target-date funds" do automatically, slowly becoming more conservative as a target year approaches. It's also connected to rebalancing — periodically adjusting your mix back to whatever your current target is.
Try It: Build Your Own Allocation
Open the simulator and build two portfolios: one that's 90% stocks/10% bonds (typical for a teen with decades to invest) and one that's 40% stocks/60% bonds (more typical for someone near retirement). Run both through a simulated crash and recovery.
Notice how the stock-heavy portfolio drops more but also tends to recover and grow more over a long horizon. There's no universally "correct" allocation — just what fits your timeline and comfort with risk.