"There will be a day when I can no longer do this, That day is not today." At I have had this thought. Is is worth it? How long can I really keep it up? Then, I realize that, the better shape I am in, the better shape I will stay in.
What people often do is they put off something for so long that eventually they will just start telling themselves it's too late. No it's never too late, a year from now you will have wished you started today.