Laura Palmer's Age

In the pilot episode of Twin Peaks, Laura Palmer's age is said once by her father.

From the script dated Dec 7th, 1988:

 INT. MORGUE CORRIDOR - MORNING
  
Dr. Hayward is seated in the corridor. He rises as Leland Palmer and Sheriff Steadman come around the corner.
  
                HAYWARD
        Leland, I'm so sorry.
  
                LELAND
        Seventeen years old.
  
Hayward puts his arms around his old friend. They embrace. Palmer pulls away.
Looks at the door marked "CORONER." Steels himself for what's coming.

Laura's age is mentioned again in the script, as news reporter Cyril Pons says the following:

        LOCAL REPORTER'S VOICE
            (voice over, on the TV)
        ... cheerleader, Homecoming Queen, most
        popular girl in school, friend to many in the
        community. Seventeen years old. Laura Palmer,
        found dead this morning, the victim of violent
        crime ...

This dialogue is omitted from the televised episode.

In the script for episode twelve (2.003, The Orchid's Curse), Sheriff Truman says the following at Leland Palmer's trial:

TRUMAN
Mr. Palmer is a well-known, respected member of this community, with a good professional reputation and established roots. And beyond that ... I'd like to say that none of us can really know what it's like to lose a seventeen year-old daughter the way he did. What that might do to any one of us ... (suddenly self-conscious) That's all.

The televised version differs, and is as follows:

TRUMAN: Your honor, Leland Palmer is a well-known, well liked, well respected member of this community. His roots go way back. His grandfather, Joshua Palmer, brought the family here more than 75 years ago *We see Leland, Sarah and Ben as we hear Harry* Your honor, no one can really know what it's like *cuts* to lose a daughter the way Leland did. (Suddenly self-conscious) That's all.

Note that Laura's age is absent from the televised dialogue. It may have been recorded, as Harry is heard but not seen. In which case, Laura's age was purposefully omitted.

In Diane... The Twin Peaks Tapes Of Agent Cooper, Dale says the following, "victim, seventeen-year-old white female."

Laura's Star Pics trading card sets her date of birth as July 22, 1972. As already stated in this post, I believe the Star Pics trading cards set the series in 1990 or 1991 rather than 1989.

Laura's tombstone has the same birth date as her Star Pics card.

I wish we could see the entire face of the stone. Since the year of her death is obscured, it may indicate that it reads '1990'. If Laura was born in July of 1972, she would have only been sixteen when she died. However, adding one year, setting the date to 1990, would match with the already given date, making her seventeen. The cards may even have her at 18 since 1991 would be the required date to place other characters at the age stated in the series. 

The first page of The Secret Diary of Laura Palmer sees Laura celebrating her 12th birthday. This is on July 22, 1984, matching with the information in the series and trading cards. As is well known, the diary continues past Laura's death (February 24th, 1989), leading one to think the diary sets the events of the series in 1990.

An advert for The Return has Laura's birthday as July 22, 1971, moving the year of her birth to match with her age at the time of her death in 1989.

The Rittenhouse Laura Palmer Memorial case topper card states Laura was born in 1971 as well.

Photo source

In Mark Frost's 2017 novel The Secret History of Twin Peaks, Dr. Jacoby states that Laura was 18. Some have theorized that Laura gave Jacoby false information in order to legally obtain his services as a psychiatrist. Jacoby also may have lied, though. One would think it would be easy to uncover the truth were the FBI or police to investigate. It may be a mistake. Or it may be the new canon.

In any case, all previous information indicates that Laura was seventeen-years-old.