Hi scsuperfrank,
I looked up your RNB and the width Dave lists on the infinity website 7'11 x 28' at 98 liters... (not 29")
That is quite a bit narrower than your SF 8 x 30 at 115 liters
That would explain why you find it quite a bit less comfortable in chop.
As to your question about age... it is a very big factor when I consult folks about Surf SUPs.
Age alone isn't the defining factor, but fitness and experience have to be blended into the equation
Your current age is also the youngest you will ever be moving forward, so boards should be considered with that in mind.
I designed a spreadsheets that I use on everyone I chat with.
It works out all the "weight to volume" numbers for me so I can evaluate the numbers on all the board in the same place
I made one up for you that I would be happy to share.
Numbers are only numbers.
They have value, but each particular board fits into the numbers differently..... many time with huge differences.
Hoppo mentioned the Ghost and the SP25, but....
I am reluctant to answer every "Which board next" post, because IMO, it is impossible to give useful answers without sounding like a promotion. Please message me if you want to discuss the SP25 and Ghost.... great boards for what you seek!
I surf Garden City, SC a few times a year, so I am very familiar with your conditions.
I'll be passing through again in May or June and would be more than happy to meet you and show you some boards.
My buddy Jack surfs SUP down near Garden City Pier. Super nice guy, you might want to seek him out to share a session!
Please tell him I said hi!!
If possible, I always do a mini demo in Garden City when I visit! (pic)