This is my neil pryde matrix 2000 boom. As you can see in the photo the rubbery part near the boom clamp is cracking a lot. I have seen this on other booms of this model. It's lasted me 2 years(the booms probably what? 20yo) with cracks but getting worse now. Is this cosmetic or is this going to die real soon. I was planning on replacing it after this season but not sure now if it will make it

I would not use it.
Temporary if you have to - put some epoxy in it and an automotive hose clamp around it real tight.
But if you do, still be ready for a swim

Back in '04 and '05 I've had this happen to two X5 booms. Within a couple of sessions both booms snapped of near the head. The 185-230 boom was a year old, maybe 20 sessions use. The second one a 155-200 just over 2 years old and used a max of 40 sessions.

It just survived 30kt gusts today with my 3.5 and foil. Just wrapped some duck tape around it and she was good to go
The water here isn't too cold yet but I was ready to swim.
My longer boom is a 2018 aluminum rs:one convertable and has metal on the arms near the clamp instead of that hard rubber that is cracking.
Next stop new boom. Thinking of going RDG Chinook alloy 135-195.

With old aluminum booms prone to breaking(mates boom snapped at the tail yesterday). How long should a new aluminum boom last
I'm only 145lbs(65kgs) so like to think I'm easier on gear than a heavier rider but pumping the sail with a foil or pumping in general seems to put a lot of stress on booms(even carbon booms).

Taping the rubber part won't help the boom snapping. The problem is that the head is bolted to a tube at both ends. The head and the tubes fit tight from the factory. However after an X amount of sessions the fit becomes loose. The play between the boomhead and the tube will worsen which in time makes the rubber crack. What however can't be seen on the outside is that due to the play either the aluminium of the head or the tube becomes brittle. It's just a matter of time before the boom will snap near the bolt.The post '05 NP alu booms have a different design. Your RS:one boom included. The 2 separte tubes are gone and a monocoque tube replaced them with a different design head clamping the monocoque tube.

I don't know how long the current alu booms last. Have switched to carbon after snapping the X5's. But I would say at least 50 to 60 sessions should be normal. However a highend carbon boom lasts many times more. I currently use an AL360 180-230 Carbon Slalom which has over 200 sessions on it. Replaced the grip and the locking pins once. Thinking of replacing it because I have the idea it's not as stiff as it used to be.