I don't really see age ratings as an issue because it isn't exactly targeting kids of today it's going after the millions who grew up playing PlayStation's. I think the listings for it already have provisional 18 ratings.
The highest age rated game on the current list 12 which is Tekken 3.
Also this is Sony we are talking about, the same company who released a games console and instead of implementing backwards compatibility(which they could). They rather you to pay £12.99 a month for a rubbish game streaming service to play previous gen games.
Sony wants to get this into as many hands as possible for all ages so they can make maximum profit. It makes business sense, so why add a bunch of adult rated games which will cut off access to certain customers when sold? Still it can be dependent on region.
If Sony cared that much about nostalgia then they would release these games in a combo collection pack for £40 on PSN and retail disk.
I love to see Tenchu on there and cut off some peoples heads, doubt it but they could surprise us!