You can get tired but try and pick up and continue. As a youth, you may at a point get tired of that project you are working on. But, your ability to pick up later and continue is what is important. Human system can be tired or get distracted at a point. But as a youth, you have to get it activated and let things start working normal again with time.
As a writer, two years back, the rate at which I published articles and books is not the same with the current. You may ask why it's so. The reason is because I am a full time permanent staff in a company. Some times after work, I feel tired to write. But the truth remains that I do not allow everything to die. I still figure out time to put up one or two articles. The only thing is that the rate at which I do that now varies.
So as a youth, you can get tired at a point but try pick up and continue. Do end up being at that spot. Slow and steady wins the race. So when you feel tired at a point, gather some momentum and then move ahead. You may not see a person that will motivate you but you have to motivate yourself.
Laziness is very bad. Do not allow it to lay some eggs into your system. Work hard to push it away when it tries to find space within you. Harbouring it within you as a youth will do you so much harms. So resist it.
Even at that point when you want to engage in that your personal work you like doing and you discovered that a force is pulling you back. Just resist the force by involving a stronger repelling force. Tell yourself that the work you want to do is more important than the laziness.
Stand up on your feet and do that which you know will pay you in the long run. You can get tired but try and pick up and continue.