After I retired.... I sat and watched TV, played on the Internet, and smoked cigarettes. After a few months of that I had gained weight, developed gout, and was short of breath.
I went to hypnotist (plus used nicotine mints) to quit smoking, went on a diet, and started doing daily Wii exercises. Then one day while out... I saw a used bicycle with a for sale sign. I bought it without a second thought.
I had bicycled before as an adult but never seemed to have time to maintain the activity. As a retired person... cycling altered my life. Now I am in pretty good shape for an old guy. I cycle 2000+ miles a year (in a Midwest cycling season). In the winter months I weight/resistance train MUCH more than summer... and cycling MUCH less. Although I still spin on a trainer a little. I walk or walk/run when the weather is decent (year round).
I use a diet app on my phone (I used to use a tablet) to watch my calorie, protein, and fat intake.
I am always looking for new "winter" activities.