Hi Diane
As your Andrew was born in 1821, possibly his father is also an Andrew Dixon, b abt 1790 ish
There is an Andrew Dixon b 1792 married Mary [Unknown] and had three daughters: -
Mary 27 Sep 1817 Rathangan RC, Kildare, Ireland: Sp: Christopher Dixon & Mary Waldon
Eliza 29 Nov 1818 Rathangan RC, Kildare, Ireland: Sp: William Hyland & Mary Daly
Bridget 27 Jan 1822 St Paul RC Arran Quay, Lincoln Lane, Dublin 7, Ireland: Sp: Rose Ferris, bapt 08 Feb 1822
So you see, there is certainly calendar 'room' for your Andrew.
However the Catholic Parish Registers of this period are often incomplete, as Catholics would not win full tolerance in their own country until the 1829 Act.
There is also a later Andrew Dixon who married Mary Gill, and they had: -
Robert, 21 Jun 1829, bapt St Bridget's RC Kill, Co Kildare, Ireland
Mary Anne, 20 Aug 1831, St Bridget's RC Kill, Co Kildare, Ireland
Richard, 06 Aug 1843, St Bridget's RC Kill, Co Kildare, Ireland
William, 25 Apr 1847, bapt St Bridget's RC Kill, Co Kildare, Ireland
The first Andrew was then a landless labourer, accounting for his perambulations, while the second was a less mobile tenant farmer..
And neither Andrew is recorded as naming a son after themselves, all other things being equal then a very unlikely occurrence in Ireland !
Both of these are distant cousins, descending from the Dixon's of Killyon, near Enfield in Co Meath.
Your best bet is to review those census records ,as the Irish are very clubbable, and often you will find relatives either visiting or indeed living nearby.
These 'additional' names, together with marriage witnesses and baptism sponsors names give you a better appreciation of their wider families.
Good Ancestor Hunting
Michael [Dixon]