"BUT I see juniors often are the ones who actually understand AI tools better than seniors"
Sorry, what does that mean exactly ? Are you claiming that a junior dev knows how to ask the right prompts better than a Senior dev ?
Speaking as a senior dev, anecdotally juniors may indeed understand AI tools better, because they spend more hours a day coding and working with the tools, and they need the tools to understand the codebase or to be productive. Seniors have more hours stuck in meetings, developing specs/tickets for the juniors, code reviewing, etc. Seniors are likely to not bother with a prompt for simple changes in codebases they already understand.
Some old dogs resist learning new tricks.
If AI is just prompts to you, you fall into the "don't know how to use it" group.
Their implication is that junior devs have more likely built up their workflow around the use of AI tooling, likely because if they're younger they'll have had more plasticity in their process to adapt AI tooling
Overall I don't quite agree. Personally this applies to me, I've been using vim for the last decade so any AI tooling that wants me to run some electron app is a non starter. But many of my senior peers coming from VS Code have no such barriers