Well, STarboard tries to build their wave boards very strong which is why you see the dur-x label on them. The ProKids boards are built as well with similar materials as in the Technora boards, but there is a bit less of it. Single sandwhich instead of double fx. But many grown up boards also use single sandwhich, so there is nothing wrong with that per se.
I use 70 myself and used a prokids EVO for two seasons until I sold it. Worked well and stood up to some serious high wind wave sailing, going on the rocks etc. But I'm not the guy to land high forwards flat...
So, if you're a smooth sailor at 65kg, I think you will get away with it. Both if you're a charger you will be safer on some of the grown up constructions.