Terry:
Many emigrants adjusted their age (older or younger) when they came to their new country. So Johanna could have been baptized in 1842. I found three possible William Skehan records on the subscription site Roots Ireland. None of the records were in Cappawhite.
Roger
First name(s)WilliamLast nameSkehanBirth year-Birth date30 Nov 1844Baptism year1844Baptism date01 Dec 1844ParishBournea and CorballyAlternative parish namesBournea, Corbally, CouraganeenDioceseKillaloeCountyOffaly (King's), TipperaryCountryIrelandFather's first name(s)MichlFather's last nameSkehanMother's first name(s)MargtMother's last nameCooperRepository
National Library of Ireland
National Library of Ireland linkhttp://registers.nli.ie//registers/vtls000634665#page/1/mode/1up
First name(s)WilliamLast nameSkehanBirth year-Baptism year1842Baptism date20 Nov 1842ResidenceMoyneParishDranganAlternative parish namesCloneen, Drangan and CloneenDioceseCashel and EmlyCountyTipperaryCountryIrelandFather's first name(s)RichdFather's last nameSkehanMother's first name(s)MaryMother's last nameFennellyRepository
National Library of Ireland
National Library of Ireland linkhttp://registers.nli.ie//registers/vtls000632691#page/1/mode/1upRegisterBaptismRecord setIreland Roman Catholic Parish Baptisms
First name(s)WilliamLast nameSkeahanBirth year-Baptism year1848Baptism date28 Jul 1848ResidenceMogoninanParishKillenauleAlternative parish namesKillenaule and Moyglass, MoyglassDioceseCashel and EmlyCountyTipperaryCountryIrelandFather's first name(s)ThomasFather's last nameSkeahanMother's first name(s)JudithMother's last nameKellyRepository
National Library of Ireland
National Library of Ireland linkhttp://registers.nli.ie//registers/vtls000632749#page/1/mode/1upRegisterBaptismRecord setIreland Roman Catholic Parish Baptisms