Separate the data into two groups as follows:
Age = randi(50,[100,1]); % Random data
Height = randi(180,[100,1]); % Random data
Weight = randi(100,[100,1]); % Random data
X = [Age Height Weight];
bins = {'normal','thick'}; % Two groups of data
Nselect = 27; % For example, you want data #27 to be a thick line
gp = repelem({'normal'},1,size(X,1));
gp{Nselect} = 'thick'; % Set #27 to be thick
p = parallelplot(X);
p.GroupData = gp; % Set the groupdata
p.LineWidth = [0.5 3]; % Set the line width
p.LegendVisible = 'off'; % Disable the legend if you don't want it to appear
