Sorry, I should expand on that. When you just have the odd grey hair, it can be quite easily covered, by whatever means you like. But once you start getting grey patches, or predominantly grey roots, you have either to commit to regular dyeing, or let it go grey. It's quite a big deal coping with transitioning demarcation lines from the roots down.
But it varies from person to person how long it takes - lots of people just have the odd silver hair well into their 40s, but most are more grey than not by 60. Some people have lots of grey in their late 20's/early 30's.
If you are fair, then highlights will work for a long time. If you are dark, you eventually have to make a choice.