I was able to get only three days swimming in a wet suit and in open water swim.
On the first open water swim I was uncomfortable with my breathing. The water was cold and I couldn't make myself exhale into the cold water. I got out about 200 yards and had to struggle back to shallow water and practice breathing. I had been warned this commonly happens even to experienced swimmers early in the season. Even so warned, it was very uncomfortable.
The next two swims did not improve AT ALL so I went into the 70.3 knowing I had never had a successful open water swim.
The 70.3 was a hard day. The 1.2 mile swim exhausted me which is the last thing I wanted to do. I finished the swim with less than 3 minutes before cutoff. During the bike ride (56 miles) I had to try and rebuild energy for the run (13.1 miles) and still go fast enough that I had time to do the run. I was successful finishing in just under 8 hours but way too tired to do more. This race was a test of my fitness and preparation for a full Ironman in August. It clearly demonstrated that my swim is far too weak for an Ironman and I don't know if I can close that gap in seven weeks.
Let me add, there is definitely a limit to how fast a 67 year old body builds fitness. I am as fit and swim as good (coming from almost a non-swimmer in September) as I could be after nine months of training. It was just enough.