I was in your boat at the start of the year, post uni but wanting to hike with folk of a similar age. If you're in the Glasgow area the club I'm in Clyde mountaineering club
https://clydemc.org/. They are pitched at folk in their 20s and 30s (I'm 25 for context).
There is also the Ramblers 'Glasgow Young Walkers' which I went along on a few meets with, their membership is a wee bit older and they do more of a mix of hills and low level walks which wasn't for me but it could be what you're looking for. The Ramblers also have 'young' clubs dotted about Scotland if you're not near Glasgow. There's also the Scottish Outdoor Young Team who operate across the country so that could be worth a look.