Hi daddy and mummies out there

my son is currently 2 yrs old but his balls (pls pardon my crude language) is still very flat and crumpled as if there is no testicles inside.
his cousin who is 4 months younger than him is already having bigger balls. Not trying to compare size here, but am worried if any of his testicals is not properly develop which might cause future complications.
during his 1st yr check up, we did bring this up to the polyclinic docter but he only said to wait and see if it develops at a later stage, now 2yrs old already still same case. Do i continue waiting?

Any parents/PDs/docters ever encounter the same situation or heard of such case? any advice would be appreciated.