while re reading your post, realized that i made a mistake in the age of your husband. His age is 65 and not 51. If he is cooperative and desire to achieve sexual strength, he can do so with above exercise. If one is healthy and the relationship is cordial, sexual activity can be resumed with exercises.
One can recover one's sexual stamina at the age 51.It is not too late. You may consult the heath care people and do the treatment. you may add the following holistic therapy.
Male deer exercise. You may help him to do male deer exercise and he may help you to do female deer exercise. this may serve as a foreplay.
You may do internal prostate massage to him.other three massages are abdominal prostate massage, perineum massage, peripheral anal prostate massage and inner thigh massage. you may Google for the websites by using the related words.
There are many yoga postures for increasing sexual stamina. You can google a phrase' Yoga postures to increase sexual strength' you may pick up any convenient exercise of massage. If it is done regularly, you may achieve your desired goal and increased health and zest in life. Wish you best of luck.
If he is interested and it just isn't rising to the occasion, he should see his doctor about Viagra or any of those similar drugs. If he is not interested, well, you have to think of some new methods, I'd guess. **? Erotic clothes? etc.