With just that much in pension, I'm worried about life after retirement.
Literal
That-much [gen-の] pension [with-では] old-age [gen-の] life [subj-が] anxious [copula-です].
ばかりの is the limiting 'only / just this much of X' used adjectivally — そればかり 'just that much.' 老後 (literally 'after-old') is the standard compound for 'one's later years / post-retirement period,' a major preoccupation in aging Japan. 不安 'anxious / uneasy' is a formal na-adjective. では here is the contrastive conditional 'with (only) that / given only X.'