Starting early makes the journey easier, less stressful, and the wealth (all forms of it) larger. If you’re not making bone-headed purchases, investing poorly, or making major relationship mistakes, you can deploy the savings into predictable (long term, not short term) passive income sources that produce while you sleep or play.

Savings combined with low fee index funds plus good debt on positive cash flowing real estate can, with time, produce a solid net worth and annual income. 

This principle is for those that can delay gratification and play the long game. Time is the friend of good investment. Reverse engineering where and when you want to arrive in financial terms can be done with reasonable predictability, allowing for less stress. 

Get your plan, work your plan, and enjoy every day. Being a ‘sit on your ass’ investor is about making a few good decisions annually, then simply waiting for the miracle of compounding to work for you. 
Less stress, less taxes, higher return. While this works with investing, this also works with you. Health, relationships, your personal psychology, and happiness all compound (in good or bad ways). The earlier you start, the better it can compound out. The best investment you can make is in continuous personal development.