There may be snow on the roof, but there’s fire in the furnace.

A proverb comparing visible signs of aging (white hair like snow on a roof) with continued vitality or desire (a fire still burning inside). The earliest located appearance is in an 1899 report about long-serving members of a Methodist women’s missionary society; later it circulated widely in newspapers and entertainment anecdotes with shifting wording (hearth/furnace/boiler).

Even if someone looks old on the outside, they may still have energy, passion, or capability.

Snow on the roof but fire on the hearth.

There may be snow on the roof, but there’s fire in the furnace.

Just because there’s snow on the roof, don’t think there’s no fire inside.

Just because there’s frost on the windows, it doesn’t mean that the boiler’s gone out.

There may be snow on the roof-tree, but there’s warmth and good cheer beneath.