I found this very easy. Solving time: 14 mins
Notes on some clues below: happy to explain others if asked.
* = anagram
ACROSS
1 S (AMOS) A SA = Salvation Army
11 TH(is) UNDER (below)
24 ALL THERE ie none here
25 CIC ‘ERO Definition is ‘old Roman’
DOWN
7 INGEST “in jest”
14 RES(PIG)HI Pig = bit of livestock in (shire)*