I'm Over 65 Yrs Old And I'm Having A Problem

I'm over 65 yrs old and I'm having a problem climaxing after an erection used for an half hour. What can I do or take or use to complete my sex experience and have a climax ?? I use a half of a levitra pill an hour before having sex !! Sorry, I thought this site WEBMD did not charge for answers to questions, I'll try the VA Hospital but I can never get a response from them. Oh well thanks anyway !