Don't sweat 18...it's just a number...it's an important number. Drinking, driving, voting etc...
Also makes you legal for all the 18+ hotties out there. Have fun!! Smile a little...you'd be amazed how much a smile helps..even if it's faked...eventually, it won't be.
As for your mother's day giftie...hmmm... the personalized card/letter will not only tell her what you feel, but give her a smile because you went through the trouble of making it yourself. Believe me...I've been making my own cards for Mother's day/wife's B-Day, kids birthdays etc... for years now. It beats the 'generic' cards like Hallmark.
Another gift- what's her hobby? Make her a few "Gift Certificates" to help her out in her Hobby/Passtime. (ie Promise of 1 hour helping her in the garden or 10 cleanings for dishes...you get the idea?) - she'll love it!