To be within reach (physically), or within one's means/ability to obtain or achieve (can afford or manage).
棚の上の箱は手が届かないから脚立を使おう。
The box on the top shelf is out of reach, so let's use a stepladder.
給料が上がって、ようやくあのブランドバッグが手が届くようになった。
After my salary went up, I could finally afford that designer bag.
予算内なら手が届く商品を探している。
I'm looking for items that are within my budget (affordable).
To be close to a certain age or milestone (e.g., 'almost X years old').
来月で二十歳に手が届く。
Next month I'll almost be twenty.
子どもがもうすぐ大学進学に手が届く年齢だ。
My child is almost at the age to go to university.