Watashi no Kokoro wa Ojisan de Aru

With no friends, family, or romance to speak of, Haruka has lived his life just going through the motions—until the day he awakens in the body of a beautiful, and womanly, dark elf! Suddenly, a world beyond his wildest imagination awaits, and uncontainable excitement races through him. There's just one problem: He gave up on putting himself out there a long time ago and has no idea how to strike up a conversation with other people. Teenagers and (other) women are certainly no exception.

But with a bottomless well of mana and a ridiculously tough body to boot, Haruka won't let any overthinking get in the way this time. Little by little, the dark elf works past his (her) fears and self-doubt, forging deep bonds with precious new friends and growing together with them. So begins a heartwarming story of an old man determined to make the most of this new fantastical lease on life!

(Source: J-Novel Club)