l just started surfing again and l am riding a board thats around 8', l ride it pretty welland now wanna transition to a shortboard, l have a 6'0 oneil rocket and l am wondering if it is too short of a board for me l am about 5'8 and in the mid 120s for weight l got the boarder when l was a bit shorter probably like 5'4 or so would it be too short to learn on or would work fine??

Given your weight, 6'0 would be a good size. But transitioning from an 8'0 to a six foot potato chip will take some work. You may feel that you're starting all over again; and in a sense, you will be. With that in mind, be patient with yourself. You already have the basic skills, so give it time. And if you really want to ride the 6', stick to it and resist the temptation to revert back to the 8'.

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You r pretty small, so 6'0'' is probably an ok board for u eventually. ( l am assuming it is a standard thruster setup, about 18.5'' wide & 2.5'' thick or something), & not a fish or anything.

It is a massive leap going from 8 foot to that though. I'd recommend getting a 6'4'' or 6'6'' with a bit of thickness first. Maybe even a bit of volume in the nose as well. You will still be able to rip hard turns on that & surf it the same way u would the 6'0 but u will paddle into way more waves & get up a lot easier. It wo not be such a setback in ur surfing as if u try to more straight to the toothpick

Well, u do have ur work cut out for you. l am sure that in the 120s the board will probably float u enough for u to take off on (provided its not on a super skinny blank). l rode a 6'4'' board for years, & l had not weighed in the 120s since about 4th grade.
l do not know what an O'Neil rocket is like (O'Neill with L is , the wetsuit company does not make any boards that l know of. l even checked on line). Your ability to paddle & take off on a board that size makes all the difference.
Over the years l have seen some folks start out surfing on short boards, & master them in a few weeks. It is tough, but not impossible. So, if u r already at home on ur 8', u will be able to do it. Just practice, practice, practice.

dude you're tiny a 5'8'' would work but get a transition board first. Try like 6'2 x 18 with a lot of volume and then move down to the fingernail.