MySQL Closest location lat/long

In Short:
I have a table called locations which stores a user_id, a route_id, created_at, lat and long. The table has around 400K rows and when I query the DB it takes about 10 minutes for it to return.

The Long:
I am trying to get routes which are closest to a user, for this I have the users current lat and long. I am wanting to get routes that have the first location (so the start of the route) within 50 miles of the users current lat/long.

I think the problem is its picking up every location and not just the single location for the start of the route, how would I target the first location? Also, when I look at what the query is doing it gets stuck in the status of moving to a temp table.

SQL
$latitude = current lat
$longitude = current long
$max_distance = 50 miles

SELECT *,  SQRT(
            POW(69.1 * (lat - $latitude), 2) +
            POW(69.1 * ($longitude - `long`) * COS(lat / 57.3), 2)) AS distance
            FROM `routes` JOIN `locations` ON `routes`.`id` = `locations`.`route_id`
            GROUP BY route_id
            HAVING distance < $max_distance
            ORDER BY rating DESC LIMIT

Code (markup):

 

Never Mind I have found the solution I needed. using the MIN mysql operator on the created_at field.