My 5 month old was diagnosed with farsighted, needs to wear glasses, r her eyes fully developed, should we wait till she's olderbefore trying glasses?

Depends. The visual system continues to develop-- establish nerve connections to the visual cortex up until the age of 9-10. The stimulus for this development is a clear image projected on the retina. Your child may have a blurred image without correction and could develop a permanent reduction in his vision because of poor development (amblyopia) have her wear the glasses full time-- very important.
Do not wait! Hyperopia is the most common refractive error of children. Children with mild (or even moderate) levels of hyperopia usually do not experience visual problems resulting from this hyperopia. However, children with moderate-to-high degrees of hyperopia are at significantly increased risk for the development of amblyopia and strabismus. Was the diagnosis was made by a pediatric opthalmologist?
Get glasses now. If she has enough far-sightedness to need glasses, then she needs them now. The glasses will need to be changed as she grows.