Well, I'm 58 and was able to do it, so I'm sure you can, too. The 400m was the toughest for me, not the distance, but the time! I do the breast stroke, really slowly. The sidestroke is the kick that the military teaches for a rescue stroke. It's better if you can do it on both sides, but, I can only do it on one side, so, it was tiring, but, it did bring my time up to a (barely) 2.
Float: You're trying too hard. It's not a tread. The first 13 minutes are just nice and restful. Be sure to take full breathes, just lie back, and if your feet sink, let them. Remember, it's just the HANDS. The best thing to do is to position your arms as close to your body as possible and just lift your hands above water, keeping them as close to your center of gravity as you can. To get your feet up, if that bothers you, do a very small kick that just keeps you moving and in the deep end!
The tired diver tow was good for me, I did finally get a 4. I found that very little buoyancy on the tired diver with a fin push works best. (Can you tell I did all of the tests several times?) The tank pull got my legs tangled up with his. I had just enough air in my BCD to let me barely float.
In the 800, be sure that you keep your fins underwater at all times. When they hit the surface, your not getting the propulsion they are designed for.
You don't have to swim everyday, but try to get some practice a few times a week. Maybe there are health clubs close that have a pool? Or YMCA?
Good luck! You can do it. I'm proof of that!!
Kathie