You only have your own experience to rely upon. This could be a real problem because if you don't have any (successful) experience to base your efforts on then you have no markers or reference points to tell you if you are doing the right thing.
You are accountable to only yourself. Having yourself as both monitor and motivator is going to be tough, really tough. You know for a fact that you will lie, whine and weasel your way out of doing things that you don't want to do (or are uncomfortable doing).
You will only push yourself so far. Experiencing intense physical effort is something that is completely and absolutely foreign to most people. Pushing your mind and body to work well outside its comfort zone is something that is scary and you will stop before you really experience it fully.
You really don't have the discipline to make yourself do it. Let's be honest for a moment. If you REALLY had the desire and the discipline to get yourself strong, mobile and healthy - then you would already be doing it.
Sounds pretty freaking dismal to me. I mean, what the hell are you going to do?
Let me make a suggestion. Let's look at the situation from a different perspective. Instead of tackling a problem, in this case your health and wellbeing, on your own, imagine you could assemble a team to help you. That team would be comprised of coaches, healthcare professionals, and people (just like you) who are trying to accomplish the same things that you are. Do you think that would make accomplishing your goal that much easier? I think it would...
Experience - If you were on a team that was led by a group of people who have over a CENTURY of experience training and transforming people; do you think your odds are better than doing this on your won?
Accountability - If you had a group of people who were as invested in your success as you are, and are going to be counting on you to show up and work as hard as they are; do you think your odds are better that doing this on your own?
Drive - If you were led by a team, who through example, will show you how much you can accomplish at any age and with any limitation; do you think your odds are better than doing this on your own?
Discipline - If you had a group of people, led by a team of dedicated individuals, that could show you how to create and foster the discipline that you need to succeed in the gym (and in life); do you think your odds are better than doing this on your own?
Let me finish with this: you can try to do this on your own and fail... again. Or you can do this with us and succeed beyond your wildest dreams. It's really up to you...