Your requirement is a little bit fuzzy. So let's look at common scenarios
In IWF, Youth athletes are 13-17, and JR are 15-20.
If in the age groups file you enable both Youth and JR, then by default
- a 13 year-old will be eligible to Youth medals. The scoreboard will show the athlete's primary age group as YTH
- a 15 year-old will be eligible to both Youth and JR medals The scoreboard will show the athlete's primary age group as YTH
- a 18 year-old will be eligible to JR medals only.
The scoreboard will show the athlete's primary age group as JR
This would be the normal behavior for a multi-age group championship.
If you want all your Youth to be considered JR, then you have to change the age boundary for JR (make it 13-20 for example).
It is also possible to create "combined" secondary categories.
For example, you could have YTH (0-14) and JR (15-20), and also a combined "U20" which would have the ages 0-20.
By default owlcms will put the athlete in the most specific category first, and then in all the other catgories that fit.
So in this second example,
- a 13 year-old will be eligible to Youth and U20 medals. The scoreboard will show the athlete's primary age group as YTH
- a 15 year-old will be eligible to both JR and U20 medals.
As a final twist, you could decide that all U20 will get their medals based on Sinclair or Q-Points or Q-Youth.