Aging, Diabetes, and Pregnancy
Both age and diabetes can affect sperm quantity and quality. Adequate control of diabetes and its complications are necessary for your husband.
I suggest you better time your sex when you have the highest chance of getting pregnant. If you have regular cycle every month, try to have sex at least two times 14th and 15th days before the next menses. For example, if the cycle is regularly of 30-day length, then have intercourse on day 15th (15th day before next mense) and 16th day (14 day before next menses). If possible, few more days around that time may help.
In the meantime, it would be helpful to do a semen analysis, to see whether there are any problem with it or not.
Hope this helps.