Found this Amber flask on a low tide here in Western Wa...the seam goes all the way through the lip indicating a more modern bottle, but the base looks odd...maybe someone could enlighten me.
I am kinda thinking 1920's? Thanks
Barnacles can grow really fast in some places. A bottle like yours, in south Florida anyway, will be completely covered in a few months.
In some island chains, nothing in a couple of years. It depends on your exact location. Look at surrounding dock pilings, or talk to people at a marina near where you found it to see how fast they grow in your area.
In Ft. Meyers there is a tourist shop on the main strip. They throw made in China knock-off's of replica 'relics' in the canal behind the shop. In about 4 weeks they have a really old looking relic on the shelf.