It's only too late if it's already budding. Earlier is better. Some people like to top right before they go into 12/12. It slows the 12hour cycle stretch when you're indoors and keeps the plants below the light.
Outdoor topping isn't as important. Indoors you want to sculpt your plant to get an even canopy of tops that fills your space. Topping is a tool to help make that happen. Marijuana always grows in a fashion where it has a spot new growth is forming on each shoot. You pinch and remove the smallest shoot of new growth. In a couple of days you will have two shoots where you snipped off the one. Essentially what you end up with is more smaller tops instead of fewer bigger ones and a shorter, bushier plant the more times this is done. Indoor light penetration is a problem so a shorter plant is advantageous to get more yield. Fan leaves from taller larger tops shade the shorter undergrowth. Scrogs are the other part of this evolution. Topping, training the shoots, and forcing them all to a spot in a grid to get an even canopy where the sea of tops aren't shading undergrowth or each other. That's how you maximize yield indoors. Outdoors is a totally different ballgame I know almost nothing about.
Great advice T-bone! Mr Baked, As T-bone said, never too late to top or fim unless into flowering. If a baby is stretching after the first 2-3 weeks of flowering , some people top the tallest shoots to stop the stretch as also stated by T-bone! great stuff! If you are not shy with your baby and really want to see her take off, top all the top shoots now and she will explode after 3-5 days. Do not get intimidated, just go with the flow and use some LST techniques to train your colas. Good babe you got there! Saludos!