I've had a few achilles issues in the last couple of years. For me, they take a while to fully heal. Sounds like you are on the right path.
As for mine, a 50 meter jog would not really have been enough to tell me if I was ready. Sometimes it would be extremely painful in the beginning, sometimes later in the run, and sometimes not until I was done running.
The trick will be for you to learn what the pain means. I would experience two kinds of pain. One pain was the kind where it was being injured or reinjured. I don't really know how to describe that too much. It was acute and felt, well, bad. Like I should stop. So I would.
The second kind of pain was a healing kind of pain. I believe this would come from stretching and working the scar tissue that had built up in the healing process. I learned this pain and was able to just run through it. In fact, it seemed to help it heal faster when I'd feel this kind of discomfort and work on it.
Massaging the tendon is good. I did a lot of that. Mostly after runs. And that would hurt, too. But it was more like the second kind of hurt.
And do eccentric heal drops. At a minimum do 3 sets of 15 drops (both legs) early in the day and again later in the day. You might notice the second kind of pain while doing these, and again, that is OK.
Heel drops, massage, calf stretching daily. 10-15 minute runs every other day and then daily when you can handle them. Slowly, very, very slowly, increase the minutes on some runs. A lot of people will say to run on soft surfaces, and I agree. But for me they needed to be stable soft surfaces. So lumpy grass or a bike path with ruts/footprints in it would be too much and aggravate my tendon.
Great advice here. I would add making sure you aren't running in 0 drop shoes. I've been struggling for almost 12 months with my right Achilles in pain. It is very slow to heal. My PT indicated 12-18 months. On month 11 now. The eccentric heel drops are essential to promote healing.