Common onions are biennial, normally flowering the second year, although unusual weather flucuations may trick them into thinking it is time to flower that first year.
Note that if you grew a hybrid variety, the seeds may not yield plants with the same characteristics as the parent.
For advice for your climate, you might check out these pages from Texas A&M AgriLife Extension:
http://aggie-horticulture.tamu.edu/archives/parsons/publications/onions/ONIONGRO.html
http://aggie-horticulture.tamu.edu/archives/parsons/vegetables/SEED.html
Common onions are biennial, normally flowering the second year, although unusual weather flucuations may trick them into thinking it is time to flower that first year.
Note that if you grew a hybrid variety, the seeds may not yield plants with the same characteristics as the parent.