I'd agree that the 1841 marriage that Roger mentioned is very likely 'your' Thomas & Mary. While the first names might not be unusual, the surnames were not that common in the area, and the combination of the names especially in the same parish you already know at least one of their children was baptised, I think makes the positive match even more definite. The sequence of children baptised to the couple mentioned shows that they were in the same parish from 1842 right through to 1863.
What source are you basing the years of birth of Thomas and Mary on ?
Most people at that time did not know their exact date of birth or age, so any most ages given will be estimates at best.
Some of my own family lived in another part of the same parish around the same time and the couple married in 1849 when they were both about 19 or 20, and had their last child when they were both in their early 50s.
The marriage records for that time dont include much detail - generally no residences or father's names,so can be difficult working back further with 100% proof. There is a possible clue in the name of one of the witnesses to the marriage - a Maria Anna Boyde... could be a sister or other relation to the groom. The names of the couple are shown in the register as Thomas Boyde & Maria Fields, the other witness is a Guielmus (William) Carton. Marriages usually took place in the bride's parish, so it's likely she lived in the parish at the time of the marriage, and possibly was also born there.
The baptism sponsors (godparents) of the children of Thomas & and Mary are also worth checking for clues to help working back further with Thomas & Mary - the godparents can be a sibling or cousin to one of the couple.