Wa'alaikumsalam
My step-grandmother was around 50 when my grandfather passed away in his mid 70's age. Not too young to being a widow. My female relatives became a widow in late of 20's age after her husband, who was in her age, passed away. She was too young to become a widow, and her husband was too young to die.
Young sister, there's no guarantee that a woman will not become a widow in young age if she marries a man in her age. How long someone will live in dunya is the secret of Allah.
I can understand if you feel comfortable with a mature man like your potential. I myself a 46 years old widower. It's okay to marry him if you sure that he is the right man for you. However, there are things you should notice. When a man enter his 40's age, his physical condition is going weaker, and his 'performance as a male' is not as good as young male. Then when you enter your 40's age, your husband will in his mid of 60's age. You should ready to take care an old man.
But like I've said, if you feel comfortable with him and you sure he is the right man for you, it's okay to marry him. May Allah bless your married life.