You need to distinguish between a private right of way (e.g. I, and my family and vistors, have a right to cross your land in order to access my land, but there is no general public right to cross your land) and a public right of way (anyone has a right to cross your land). In this case, obviously, you're talking about a public right of way.
A public right of way can arise in various ways — e.g. where the local authority makes an agreement with the landowner to create a public right of way on his land. But presumably that hasn't happened here.
In this case, you'd be arguing that the right of way has arisen by dedication — the landowner has made his land available for use as a public right of way, and the public has accepted this by actually using the land for that purpose. Long use by the public can be treated as evidence creating a presumption that the landowner did originally dedicate the land.
There isn't a clear fixed rule about how exactly long the use must be, but in this case it has been going on for more than 30 years, which is longer than has traditionally been considered necessary. Plus, someone has taken some basic maintenance steps by gravelling the path and (presumably) the landowner didn't object. And I assume it's a well-defined path with definite start and end points; it's not just an open space that people cross wherever they like, and in whatever direction they like. So I think there's a pretty good case for saying that there is a public right of way here. (Of course, I haven't heard what the landowner would say to oppose that; there may be other facts, not mentioned in the OP, that the landowner would rely on.)
If a public right of way exists then, under the Planning Acts, it should be included in the development plan and shown on the development plan map. So the first thing you should so is check the current development plan for your local government area and see if the right of way is shown.
If it is, great. If not, you (or, better still, a community group or organisation of some kind) should approach your councillors about getting it included. The Council may be a bit resistant because they will have to serve notice on the landowner, invite objections, etc, and this may provoke a bit of a row that they would rather avoid. Plus, they may fear that the call to have it mapped will be followed by calls for the council to pave it, fence it, provide lighting, etc. So you might have to campaign for this.