HOBBIT AGES
Hobbits live slightly longer than Men, usually around 100 years.
Hobbits also take a longer time to grow up and are not considered of age until 33.

A Hobbit in their 20's (or tweens) is the human equvilant of an adolescent.
A 33 year old Hobbit would be the equivilant of a 20 year old.
A Hobbit in his 50's would be considered in his prime.
A Hobbit in his 70's would be considered middle aged.

From my calculations I would say that a Hobbit around 12 would resemble a human about 6 or 7

AGES AT THE TIME OF STORY
Drogo Baggins 72
Primula Baggins 60
Frodo Baggins 12

Bilbo Baggins 90
1st cousin once removed to both Primula and Drogo
2nd cousin to Frodo

Rorimac Brandybuck 78
Master of Buckland
Oldest brother of Primula Baggins
Father of Saradoc Brandybuck

Saradoc Brandybuck 40
Nephew to Primula Baggins
1st cousin to Frodo Baggins
Husband of Esmeralda Brandybuck

Esmeralda Brandybuck(Took) 44
Sister of Paladin Took
1st cousin once removed to Primula Baggins
Wife of Saradoc Brandybuck