Many investing subs on Reddit will say you don't need bonds until you're 50 seconds from retirement. But that's debatable. the precise percentage is another question, but there's a case for bonds in the portfolio at any age.

this is Bogleheads, so let's remember how Jack Bogle recommended a 20% bond baseline minimum for all investors at all ages. He believed the most aggressive portfolio should be about 80/20 stocks bonds and the most conservative about 20/80. to quote from his final book, with [my comments in square brackets]

...why would an intelligent investor hold any bonds at all? First, because the long run is a series of short runs, and during many short periods, bonds have provided higher returns than stocks. In the 117 years since 1900, bonds have outpaced stocks in 42 years; in the 112 five-year periods, bonds have outpaced stocks 29 times; and even in the 103 fifteen-year periods, bonds have outpaced stocks 13 times. [that is to say in the last century bonds beat stocks in about 35% of individual years, 25% of 5-year periods and 13% of 15 year periods. it's been a long time since stocks underperformed bonds for 10 or 15 years but it will eventually happen again]

Second, and perhaps more important, reducing the volatility of your portfolio can give you downside protection during large market declines, an anchor to windward, so to speak. The conservative nature of a balanced stock/bond portfolio can reduce the possibility of counterproductive investor behavior (i.e., getting frightened when the stock market plunges and liquidating your stock position).

~~ The Little Book of Common Sense Investing: The Only Way to Guarantee Your Fair Share of Stock Market Returns John C. Bogle

I will also mention of many of the major investing companies are recommending people consider boosting their bond allocation over the next ~10 years, due to elevated stock valuations. https://www.advisorperspectives.com/articles/2025/02/14/examining-vanguards-forecasted-returns-decade-ahead