My son is 19 months now and we've travelled with him since he was 4 months old.
In my experience, the older they get, the harder the holiday.
We took our son on a cruise when he was 11 months, and walking, and he was all over the place. We also took him away when he was 4 months old and it was SO much easier since he didn't crawl or walk.
I hope this helps.
xx