My boys are 18 months 4 days apart, it was hard at the start (DS1 did not start walking till 21 months so hard getting anywhere etc.
They r cute when they play together and DS1 gives DS2 hugs and kisses all the time.

I think all kids and all parents are different and there is not a right time I have friends with 12 months gaps up to others with 10 year gap.