I had 2020 vision till 2012 (39 years old then). I am convinced that my myopia onset was perceptibly accelerated with the purchase of my first "smart phone". And the constant use of it: Whatsapp & twitter. Can the damage be reversed?
Your body changes a lot around the 40 year mark and I don't think that it's related, at all, to your smart phone. I'm sure that those older than us can tell us what to expect in the next decade.