Old Forum Software and SEO

[escape2k]

I am still using Old Forum Software like
vBulletin 2 & 3
phpBB 2
Burning Board 2
and the like.

I cant help but i still like the old Software better than the new ones.
So i keep updating the old ones to new PHP/MYSQL Versions and the like.

There is only one thing the new systems do better in my opinion:
They have responsive templates, i do not care personally but a lot of people seem to visit and posts through their phones today.

So i am thinking of making the Themes from some of my old Forums Responsive.
For vBulletin 3.8.x i do not even have to do it, its already available to buy:
https://www.sultantheme.com/forum/?styleid=52
https://www.sultantheme.com/product/st-vb3-responsive/

But there is one thing.
I know almost nothing about SEO.

So the Question that bothers me is, the templates are very old (just look at the source code) and therefore different than those of modern software. Today people are using divs a lot and back than there was extensive use of tables for layout. (which i like better by the looks but its dated today)

So the question is, does the dated Templates have negative effects for SEO or not?
Ofcourse their are alot of other things for SEO also, i just want to know if the templates would be a Problem, and if so how much of a Problem.

Thanks,
escape2k

PS:
Please no "you should really upgrade" posts, thanks.