slow postgres performance with simple querys

After a lot of reading I found multiple sources saying Postgres should be able to handle ~100 million rows. I set up a simple table with:

CREATE TABLE trade
(
    id INT PRIMARY KEY NOT NULL,
    symbol VARCHAR(),
    open_time TIMESTAMP,
    end_price INT
)

I have 12 million of these records. My simple query of

SELECT * FROM table WHERE symbol=x and open_time>start_time and open_time

This query always returns less than a 1000 rows yet it takes 1100 milliseconds. This seems like a lot for a simple table with 10x less rows than it should handle? Although I don't have any indexes cause I don't know what would be the best indexes to put on this table. Is it possible to get this down to 100ms? Any help writing a more performant query or db would be appreciated EDIT 1: After reading the comments I put the following indexes on the table

CREATE INDEX open_time ON trade(open_time);
CREATE INDEX symbol ON trade(symbol);
CREATE INDEX end_price ON trade(open_price);

After adding this the query time is 240 ms is this the max? Although I have noticed querying the beginning 40k rows the query time drops to 60ms after that is rises to 240ms what is causing this?