QLite3 has some cool new date functions. Per the docs site you can use date(), time(), datetime(), julianday(), unixepoch(), or strftime() depending on how your column data is formatted.
If you use strftime(), like my suggestion below, then you have to make sure that your column data is formatted the same way as your strftime string.
You would probably want something like:
SELECT * FROM mytable WHERE dob < strftime("%m/%d/%Y", 'now', '-30 year');
Note that you might have to change the format string here to match your own.
And here's some code that I use personally to give you a better idea of how powerful it is. It lets me get all the orders from the previous 3 months, not including this month.
SELECT * FROM orders WHERE SHIPPEDDATE > strftime('%m/%d/%Y', 'now', 'start of month', '-3 month');
The modifiers are very powerful with sqlite. The first string inside strftime() is the format, the 2nd string is when you want the date to start. 'Start of month' puts the day to 1, and '-3 month' goes back 3 months. So if I ran that today (08/03/2022), the date it uses would be 05/01/2022.