Can I paint directly over 50 year old paint?

[wannabeabuilder]

I am in the process of stripping some wallpaper. Underneath to my luck the wall is coming up very smooth. After stripping the paper I am also wiping with a wet rag with some detergent to get the adhesive off - well more like scrubbing. Some areas are more yellow than others so I am guessing the yellow bits are adhesive and I have been unable to get the adhesive off 100%.

1)Do I need to wet wipe/scrub more vigorously and try to remove the yellow (adhesive?) bits 100%

2)Can I paint straight over the underlying smooth painted surface or do I need to use a primer first?
I am guessing that this underlying paint is from the late 60s or maybe 70s. Just a guess. If I'm wrong then at most from early 80s.

Thank you!

 

[Pigeon85]

Give the wall a bit of a sand, then put a coat of oil based undercoat. Emulsion straight onto this.

 

[emilybronte]

You could get through a lot of oil based undercoat - hope you can keep the windows open, or you could end up feeling very ill!

If it's a large room I'd suggest Zinsser Gardz as an alternative to o/b undercoat. Probably cheaper, faster-drying and just as good as a sealant.