Regardless of the exact reasons why plasticity declines with age, it's obvious that any fix is a long way off. I wouldn't take this news as positive, rather negative, actually, since it just means we have yet more work to do
Like, instead of saying "I always lamented the idea that as we grew older we generated less and less neurons" the GP can now say "I always lamented the idea that [other unknown mechanism behind declining plasticity]". Hardly good news.