I have had a challenge in mind for some time now and that is to be fitter / faster at forty than I was at thirty. This isn't a comparison between super heavy me and now. No, it is a comparison with how fit I was aged 30 (a good few pounds into my weight loss and exercise journey) and how I am when I am 40 (in a couple of years time). This will involve beating as many marks set in my 30th year as I can in my 40th.
It sounds simple, it sounds for me do'able, though the marks I set at 40 will be a fair bit tougher to beat when I'm 50 simply from the point of view of my being a late starter fitness wise. Still I might take that challenge on too, why not?