Men can continue reproduction throughout their lifetimes as sperm production persists. Men of advanced age may experience a decline in sperm motility and volume, but they can still get their partner pregnant. The number of sperm men produce stays steady throughout their lives regardless of age.
There are some studies linking the age of a male partner to miscarriage rates. However, the studies utilised a very small sample number and the female partners in the couple were also of advanced age.
This suggests that perhaps men should be younger when trying to conceive, but the results are not definitive.
Generally speaking, the best age for getting pregnant is highly subjective and varies from individual to individual. Whatever age you and your partner feel ready is the age you should begin trying to become pregnant.