I will have an engorged penis & a couple of minutes after putting the condom on mr. happy becomes mr. sad & the party is over. I will admit that this is my first experience with condoms at the age of 70. As soon as the condom is removed & oral manipulation is applied......nirvana. Is this common for older men? Is the condom actually preventing blood flow? It is a little discerning not to be able to complete the task at hand other than orally.

There is a lot of info on this in the 60 and over board
Many people have condomitis
Find a provjder who uses the female condom

I have no idea what brand you're using. Since providers usually furnish the protection you're at a disadvantage, but if you find a brand that works, get the name and then buy them on line.  Many escorts will let you byoc as long as it's in an open box.  And yes it's common if you've never used condoms, to have issues.

In my case it started to become an issue after I hit 50 or so. I thought it might be an issue of losing sensitivity, but I don't know, maybe the pressure of the condom tends to push blood back out of Mr. Happy?

try different ones and road test them at home watching some good porn.

I always bring my own condom! I also had the problem once, so I switched to larger thinner styles like Magnum bareback or Skyn large! Worked wonders.