Mr. Wickham’s exact age is never explicitly stated in Jane Austen’s ‘Pride and Prejudice’, but we can infer some details about it. It is generally believed that he is in his late twenties, around 28 or so, at the time the events of the novel take place.
This estimation comes from the context of his character and his relationships with other characters, particularly with Mr. Darcy. Wickham is portrayed as a charming young man who has experienced some life challenges, which suggests he has had enough time to reach adulthood and be involved in the social circles of the novel.
Furthermore, considering the typical age for men to be considered mature and capable of social maneuvering in that era, a late twenties age seems fitting for Mr. Wickham, allowing him to be both youthful enough to be seen as attractive and ambitious, while also seasoned enough to have developed his somewhat dubious character.