The smaller size of both testes and genitals would be most probably from birth and would be genetically determined or due to some cause when U as a baby were developing inside u'r mother's womb. Most probabby U will be perfectly normal sexually and U should have a semen analysis
to find out its adeqacy for fathering a child after marriage.Reg. treatment, possibly some hormonal
administration by a qualified specialist may help to some extent. Sometimes, artificial testes are implanted, but purely for cosmetic reasons.