My aches and pains have nothing to do with lifting improperly. After years of hopping in and out of a truck up to 100 times a day, sometimes more, your body starts protesting. Compound that with having a route with tons of 4 story apartments (no elevator), and a blown out knee from said apartments, it's slow moving when I first stand up after sitting for a while. And I'm one of the lucky ones. I'm fortunate that I've never hurt my back in all my years, because I knew as a single mom I couldn't afford to be out on WC, so I was always very careful.
Ask anyone at FedEx who has been around more than 10 years about their aches and pains. Trust me, you will be hard pressed to find more than a handful without any. Hopefully, starting out at your age, you will be one of the fortunate ones too.