Where in Wales?
Main differences as far as I can tell:
Education -letter grades for gcse, AS levels still exist. No SATs but there are literacy and numeracy tests every year I think from year 2 to 9. But they are done online and most schools don't make a big thing of them or revise, so a very different experience. Education compulsory to 16 not 18. Free lunch and often breakfast clubs in primary schools. As others have said student loan structure a little different. Welsh compulsory to 16, but experience of that will vary massively by area and school.
All documents, signs etc bilingual. But far more non Welsh speakers nationally than Welsh speakers. However, in certain areas, mostly rural north and west, Welsh speakers are majority and not many English medium schools. In the south and cities far more English medium than Welsh medium though.
Extra layer of government with Senedd, so more voting to do, and Senedd elections can vote from 16. Health and education devolved, not sure what else. But I think most home office and economic policies still come from Westminster.
Like England, it's very much not one homogenised block, so will depend where you live. One reason I'm not a Welsh nationalist is that, living in Cardiff, I really don't feel I have more in common with someone in north Wales than I do with someone in say, Bristol or Birmingham, culturally or politically. Yes I like some of the history and traditions, and feel a sense of belonging, but then if you moved to Cornwall or Yorkshire from London you'd have a similar change of culture, traditions etc id imagine.