I think you're right; the suspect is young, around the same age. And if they have the suspect's DNA (which I believe they do), it could be difficult to match because the suspect hasn't committed any crimes or submitted DNA to 23andMe or any other ancestry databases, for that matter.
I'm 36 and did my genetic testing with 23andMe at 27. Are younger generations using genetic testing services? It was all the rage with my generation.
Solving a murder using Genetic DNA doesn't involve the murderers DNA being in the database at all. As a hobby, I find people's biological families. They submit their DNA then you divide their matches into 4 groups, one for each grandparent. Then you use each branch of their matches to build a family tree. Where it converges is where you'll find their biological parent. You never know how long it's going to take. I found one person's dad in 24hrs and she's been searching for 20 years! I'm working one right now that's super difficult, I've been at it for over 6 months. Of course, when someone is doing it for LE they have many more resources available.Exactly re your first paragraph.
Regarding young people and genetic testing, I think many are paranoid about having their DNA out there. MOO.
(And I'm not tooting my own horn, I've done genealogy for 20+ years, anyone can do it once you learn the ropes)