My own view is that they earn spots based on merit, the same way all us old buggers did.
You start by asking at your local Soul night if you can do the early set, you go anywhere they offer open deck spots, you travel anywhere to do a spot, even if it costs you more than you get paid. You play the best set you can, everytime you DJ.
If you are good enough as a DJ, and have interesting enough records to play, you will start to get bookings. It is not an instant thing, you have to earn the respect of others, and the best way to do that is be a good DJ, playing good records. What you have to remember is that promoters pay you to make a success of their night, so they will not pay someone who is useless, or doesn't have good enough records.
Back to the original question. Should people get spots just because they are young ? No of course not, you might as well say should people not get spots because they are old and bald ! Age is immaterial, they deciding factor is how good they are, and the records they play.