A 2016 study (Vaquero and colleagues, published in NeuroImage) compared 36 expert pianists with a group of non-musicians. Among the pianists, those who started before about age seven played scales with more precise timing, especially with the left hand, and their brains showed some structural differences from those who started later.
What the study can and cannot say
It is an observational study of experts, so it cannot say that starting early causes these differences. It does not describe beginners at all.
What it means if you start as an adult
It says nothing against starting at 40, 60 or 70. The trials with older beginners, described in our article on piano after 60, found gains after a few months of regular lessons. The size of the benefit may be smaller than for a child, but it is not zero, and the enjoyment does not depend on it.
Frequently asked questions
Is it too late to start piano as an adult?
No. The studies on early starters compare experts and do not show that late starters cannot learn or benefit.
Do early starters have bigger brain changes?
In this study, early and late starters differed in some brain regions and in timing precision. It cannot show cause and effect.
What matters most for an adult beginner?
Regular practice over months. The trials in older adults ran from four months to a year.