I used to do a lot of chin-ups when I was younger. I had a bar at the doorway to my room and used to do a couple of chin-ups whenever I walked through it (or rather swung through it). At my best I could do couple of dozen chin-ups in one go. I think my record was 27. I was also able to do a few ones with 20 kg extra weight strapped to my waist. I was never really fit in general, it was just the combination of doing that regularly and weighting way too little.
Those days are long gone. I haven't been doing chin-ups regularly for decades and I constantly carry that extra weight (and some more) with me. Still, I thing there has never been a time when I couldn't do at least one chin-up. I haven't been able to do dozens in decades either, but last time I took exercising seriously I was able to get back up close to ten.
After the past few months of inactivity I don't think I can do more than a few anymore. But I do want to. Besides it's easy and effective workout, better than nothing.
So what I have decided is to do 1000 chin-ups. Not at once (obviously), not daily or otherwise regularly. Just whenever I feel like it, at my own pace. It could take three years if I do one per day, a year with just three each day. It doesn't matter. Only thing that matters is that I'll start keeping count. And then, one day, that count will reach one thousand.