Never had premature ejaculation problems but now... ?

I'm 54 and have been having sex for the last 40 years. I have never in my life experienced any erection problems. I was able to hold myself....... Now I have recently remarried and my young wife is very attractive........ I can only take 30-40 seconds inside of her and then I have to........... its not in my control anymore... This is very frustrating.. Have tried masturbating beforehand but this means I"m unable to get an erection for 2 hours. She seems to want sx every night. She is 19 and I don't want to disappoint her. What can I do ?