French adjectives agree in gender and number with the noun they describe, not with the person speaking. Most add -e for the feminine (petit → petite) and -s for the plural (petit → petits, petite → petites) — a masculine plural adjective takes just -s, a feminine plural adjective takes -es.
Adjectives that already end in -e in the masculine don't change at all in the feminine (jeune → jeune, un jeune homme, une jeune femme). Others have irregular feminine forms that have to be learned individually: beau → belle, nouveau → nouvelle, blanc → blanche, long → longue.