I also started to experience similar problem. Gradually got worse. Replaced clutch master cylinder with no improvement, now no gear is possible to engage. Researched the problem and looks like clutch slave cylinder is the problem. Major DIY project, and very expensive garage repair due to labour time involved.
Could just be your linkage is a bit stiff. Can you engage gears when engine is off? If not, it could be the linkage just needing some cleaning and lubrication. Otherwise it could be the slave cylinder.