I see the marriage of Owen and Margaret on the 24th November 1862 in Saggart/NewCastle-Lyons Catholic Parish South County Dublin see the right hand page in this section of the marriage register, there are no residences noted for the couple, the witnesses appear to be a James Simons[?] and Ann Simon.
There are a couple of Glynn/Glyn baptisms in the parish, both both girls baptised to two different couples - Bridgit (Brigida) baptised 1841 to Laurence Glyn and Mary Tyrell, and a Mary (Maria) baptised in 1835 to a Samuel Glynn and Mary Tyrell. There doesn’t appear to be any Glynn baptisms around the 1st January 1839 - the register for that timeframe is available at this link.
Extending the search to include parishes adjacent to Saggart/Newcastle-Lyons, some of which extend into counties Wicklow and KIldare, doesn’t show any additional possible matches for Owen. Note the Christian name Owen can be recorded as Eoghan or the Latin form Eugenius.
The Saggart baptism registers go back to 1832, but some of the adjacent parishes have registers that start later - e.g. Kill (Kill & Lyons) Co. Kildare 1840, Blessington 1852 etc. It’s quite common for secondary sources of dates, e.g. census returns, death certs etc, being inaccurate, sometimes they turn out to be the wrong year, and other dates just estimates or saints days (e.g. St. Patrick). Note the Catholic registers for this timeframe usually just record the baptism date, and not the birth date.
Do you have any additional details on Owen's sister Mary - e.g. estimated year of birth etc, where and when she married ?
If she married in the US her record could include parents names, similarly a death cet for either of the siblings…
It would be worth recording the details you have for your Owen and Mary on our Ancestors Database - that way anyone else that might be researching this family could find the details, and hopefully make contact.