Synonyms of "Not old" are words such as young, new, early, modern, contemporary etc.
or specifically in reference to age: juvenile, little, youthful, junior, etc.
Old Octogenarian
Another word is but
another word for very large
another word for the word suffice is- be enough
Suggestion is another word for proposal answer: engagement?
Another word for not old is young.
"Ancient" is another word for very old.
Another word for 40 year old is 4 decades. 8D
Another word for an old female cat is a grimalkin.
old
aged
old, decrepit
Elder
Old, retro
ancient
old-fashioned
old, gothic