Unfortunately their doesn’t seem to be a work around you can order a vehicle and as long as handover date is either on or after the 25th birthday it is possible. If there is only a couple of months difference it might be an idea to hold off and use the allowance in the meantime to hire a vehicle. Some of the big hire companies do a reduced rate for a 3 month hire period within reach of the allowance amount. Then order a vehicle with a pick up date to coinsude with being classed qas over 25. And with motability unlike some insurances you are classed as over 25 upon I minute passed midnight on the day of your birthday, some 3 month hires can workout as little a £6 a day with a wide choice of vehicles available at £9 a day. May tide you over until your partner turns 25 and the choice widens.