I agree, I am 66, so I set my screen resolution to 136x768. That makes everything larger.
Also under system>Control Center>Look and Feel>MATE Tweak>Windows>Windows manager what is your setting? I have mine set to Marco (no compositor) but you might want to set your to Marco (Adaptive compositor). Using a compositor can affect the size of the scroll bar.
"If you have trouble resizing windows with the mouse, because the resizing borders are too thin, option "Marco (Adaptive compositor)" can help."
Options "Marco (No compositor)" and "Marco (Compton GPU compositor)" give you extremely thin window resizing borders that are hard to hit with the mouse.
Many users do not know or do not want to use the "Alt+mouse" window resizing method. Besides, if you are using a laptop touchpad or a remote desktop session, resizing windows with their borders may be the only comfortable option.
I have collected detailed information about window resizing issues here: