That's somewhat misleading. What is true is that age 70-1/2, they must start withdrawing a fraction of their traditional IRA, traditional 401K, 403B, etc. every year. This does not apply to Roth versions of these assets.
However, this does not oblige a stock sell-off.
Because nothing prevents the owner from simply selling the stock in the IRA, withdrawing the proceeds, and then using the money to re-buy the stock. This isn't a wash sale because the tax treatment of the two assets are different.
In fact, a smart retiree may well have already done this for tax reasons. Suppose retiree has $25,000 in an S&P 500 index fund at age 60. In the following 15 years, it grows to $100,000.
- If it is left to grow in the IRA account, and withdrawn at age 75, the growth is taxed as regular income when it is withdrawn, e.g. In a 25% bracket, tax is $25,000.
- If it is withdrawn at age 60 and placed in a normal brokerage account in an S&P 500 index fund, the 15 year growth will tax at the 10-15% long term capital gains rate. Tax at age 60 is $6250 and tax at age 75 is $7500.
So it is advantageous for a person to pull stocks out of a retirement account and re-buy them in a normal way.
A well-managed fund will have less of these, anyway.
Good investment practices call for moving a retirement account away from equities and into less volatile investments. That is to prevent a situation where a stock (or the whole market) takes a major hit, and the market does not recover before the retiree needs the money. At 70-1/2 this move-away should be fairly well along. So accounts subject to this mandatory distribution should not be "loaded with stocks" anyway.
However, if an account had an S&P 500 index fund that the retiree was forced to sell, and the retiree's strategy did call for being in the market, they would simply buy a similar amount of VOO in a regular, taxable brokerage account, as discussed above.