"Years, months, weeks, days and hours."
Translation:Blianta, míonna, seachtainí, laethanta agus uaireanta.
ae is treated as a single broad "digraph".
It is fairly rare, but apart from laethanta, the other common example is Gaeltacht.
Aeráid, traenálaí and aerfort are some of the ordinary, but slightly less common, words containing this broad digraph that you will encounter in exercises on Duolingo.
(This isn't considered an exception to leathan le leathan, caol le caol, as ae is always considered leathan).