There are lots of "weird old tips" for getting healthy around the web. Slate writer Sarah Wildman has the privilege of having a father in his 60s, who has done the exercises almost every morning and looks the part today.
J.P. Müller's My System, first published in 1904, focuses on core muscles and general dexterity, and is done over 15 minutes. So it's not exactly modern and includes the crunches that some have sworn off. But Wildman's father, now a physician, has stuck with the system and seems to have done well by it. He also recommends elements of My System to patients with back pain.
It may not work for you, and you might prefer to work on building muscle mass through more modern methods. But it's worth checking out a system that's stood up fairly well against the test of more than 100 years.