The search function here is in fact terrible. I won't waste your time enumerating my reasons for saying so. One example: since every post with a search word is included in the results, a single long thread may "use up" half of your 100 search results.
If nothing else, the function leads to a lot of wasted time.
As Donna says and you are doing, use the "Advanced" feature and select "newer than 5 years". If the 100 results are all too recent, note the date of the oldest one and search again with "newer than 5 years" and "older than..." the date of the oldest post in your initial search.
