I'm thinking you should be able to harvest some, put it in a specimen jar, and have your urologist examine it. Also, have him / her evaluate some of you regular ejaculate to help be sure they are different and healthy.
I spoke with my urologist this morning. He said it was pre-cum. I said no no no, I’m in my fifties and know the difference! My wife can be sucking and get a mouth full before I’ve orgasm’d. I can be masturbating and cum all over my belly, and I keep going for about 30 seconds until I have my climax. It’s not the worst thing that can happen, it just seems really weird. Even stranger that doctors aren’t familiar with it. He said it may be my meds, and he could be right.
It’s probably just PreCum indicating that you are healthy
So to be sure I understand - you partially ejaculate before you orgasm, and then ejaculate the rest with orgasm? This probably isn't anything to worry about, but since it's new for you, you should talk to your doctor to rule out any issues.
At age 55, you should be talking to your doctor about your prostate, your risk factors for prostate cancers, and whether or not a PSA is right for you. If you haven't done this yet, now would be a great time. :)