Hi Ang, there are 3 Thomas Ryans married in Dublin in 1859, one says full age so assume over 21, I was going to use the fathers name to search for a birth but that scuppered that. You can see the marriages here, select church records and Dublin. If you know the spouses name it will narrow it further. https://churchrecords.irishgenealogy.ie/churchrecords/
Ryan is a common name and found mainly in Tipperary / Waterford area so even with fathers name it will be difficult as you will find a lot of Thomas Ryan's in my opinion.